What is your favourite Open-Source game?

Battle for Wesnoth - a turn based tactics game in a fantasy setting. It's also available on Steam and itch.io. Coincidentally, version 1.18.0 was released yesterday.
- This! I have so many fond memories of epic Battle for Wesnoth sessions with friends. That was back in High School, 12+ years ago, I still have the itch to boot it up again.
- I wish that the original use-case for Battle of Wesnoth's engine, Wargus, was still being actively developed
  
  Wasn't Wargus an StarCraft like engine?

Roguelikes: DCSS, Shattered Pixel Dungeon, Nethack
- I play shattered Pixel dungeon on my phone once a day it's good but I really never get past the mining stage and can't understand the crafting.
  One day I'm hoping for a fluke we're I somehow go on to beat it but anytime I actually feel like my characters getting good I die in seconds to something.
  Good game though it does give you the hope you just need a lucky run.
  
  I've been playing Shattered Pixel Dungeon virtually every day for years, through I don't know how many updates. I'm far from convinced that every run is winnable, but there are some patterns that I've observed.
  Mage and Huntress seem to be my best classes. The Mage's staff means that you are guaranteed to have something that's worth upgrading. The Huntress' bow and her special abilities like growing grass by walking can make for some truly interesting gameplay changes, whereas I feel like most of the other classes' abilities are more about moderate improvements to quality of life.
  A Ring of Haste is probably my favorite ring to find, since being able to kite monsters is a great path to victory. Tenacity, Elements, and Strength are boring. Wealth can be good if it comes upgraded, but I wouldn't put scrolls into it. Evasion always seems to turn on me sooner or later. Energy and Arcana can improve quality of life but are otherwise pretty mid.
  A Wand of Regrowth is almost always a path to victory, especially if it comes upgraded, doubly so if you become a Warden, and triply so if you can combine it with the Sandals of Regrowth.
  A Wand of Blast Wave is incredibly useful when used to knock enemies off ledges or into traps, saving yourself the trouble of killing them.
  Other wands are a super mixed bag, depending on what you can manage to do with them, but I'll say that some of my most fun and successful runs are putting a Wand of Corruption into my Mage's Staff and becoming a Corruption Battlemage. You whack an enemy, Amok him on his friends, then corrupt them, then rinse and repeat until you win.
  I've already mentioned the Sandals, which I'd say are incredibly useful if you've got a Wand of Regrowth or a Blooming enchanted weapon, but are otherwise hard to keep getting enough fresh grass to make worthwhile. I think the Ethereal Chains and Hourglass are my favorite and most useful artifacts. Horn of Plenty is okay but not great, unless you can combine it with being filled by the Battlemage's energy generating ability. Other artifacts are mid, but I'll make a special mention of the Unstable Spellbook which seems to screw me as often as it helps and yet I can't deny that I have a great time with the mayhem it adds to my run. The Alchemist's Toolkit is terrible; I hope a future patch significantly alters or replaces it, because honestly why bother using it at all?
  I think my favorite runs are Corruption Battlemage or a Sniper with a nicely upgraded Boomerang; I always get a lot of fun out of using the boomerangs.
  There's no end to the conversation but that's all I've got for now. It's far and away the most played game on my phone... possibly my most played game ever, measured by eternal hours. The publisher is an absolute treasure and he deserves all the praise and success in the world.
- DCSS has been one of my automatic installs on any PC I have for years now.
- They ever end up taking magic dart out of dcss?
  
  Story?

Right now I'm basically playing Beyond All Reason almost every evening. It's a game in the Total Annihilation "tree" of games. A massive scale RTS. I previously played Supreme Commander and Planetary Annihilation, both of which are also inspired by Total Annihilation, but I have to say that BAR is really better than both of them. I almost can't believe it's an open source game. It's still in alpha, but it's been way more stable than most AAA games I've been playing recently.
- You shold look into zero-k as well. I started out with BAR but found out zero-k more engaging
  
  Could you elaborate on why zero-k is better than BAR in your opinion?
  
  That's a continuation of TA Spring? Neat, played that a looong time ago.
- Never heard of this and I'm a big fan of the TA/Sup Com series. I will try it when I get the chance. Thanks for sharing!
- Sounds amazing thanks!

I've gotten all my friends hooked on OpenTTD multiple separate times

Endless sky. You start off with a single spaceship and fly around the galaxy trading, fighting pirates, and buying/capturing more ships. The devs are still regularly adding new content too.
- They've been working on the Hai storyline a lot, and last time I played there was a lot more in Coalition space.
- Endless Sky is amazing. I've put so many hours into it. It's available on Steam or as an AppImage from https://endless-sky.github.io
- I love this game too, I was deeply into all three of the Escape velocity games as a kid and Endless Sky scratches that itch perfectly

Unciv is a Civ 5 remake with simplified graphics. Its a lot of fun but the AI is brutal.
- Tried this just couldn't get past the tiles I'm probably spoiled from playing civ on pc but yeah I tried quite a few tilesets and nothing worked for me
  I suspect the actual game is probably better than the official ones but I just couldn't get past the graphics.
- I play king and lose 9/10 times. still great
- Unciv is pretty cool but the simplified tiles and buttons can make me feeling a little lost and feel like I'm missing stuff at times

Does DOOM count? It's been officially open sourced recently, even though it was already treated as such for decades.Either way, I can't stop playing it, there's 30 years of user created content to go through.
- Id Tech 1 (Doom) source has been available since 1997 under a restrictive license and under the GPL since 1999, so not "recently". But yeah, that's my answer. Original Doom.
- That's what I'd go with it. Came here to comment it, but I was beaten to it. There are so many great ways to play through it, as the modding community has made so much amazing stuff over the years.

Mine is Mindustry too
OpenTTD is also nice
- OpenTTD is awesome, especially when you dive into the NewGRFs (mod content)
  Simutrans is also pretty cool. Similar game but definitely makes some different choices that make it play differently and has some nice features that will probably never make it into OpenTTD
  
  Simutrans is also pretty cool.
  Looks interesting, I'll check it out. Thanks!

In my AP Computer Science class in high school, every now and then our teacher would give us a free day. We would sit around playing Unreal Tournament on the LAN.
At one point the teacher decided he wasn’t comfortable with a game with guns in class.
So…I got everyone to install Cube, the open source first person shooter. Specifically a copy of it where I had removed all of the gun models. So we just ran around punching and bullets would fly from our fists. Or, in the case of the rocket launcher, an exploding sofa would fly from our fists.
I don’t know if I would call it my favorite, but we had a lot of fun with it.

Battle for Wesnoth. There's several FOSS games that are pretty good, but BfW I've played the most.

openttd is great

Someone on lemmy a few months ago mentioned this rts beyond all reason. Since then I've easily put 100 hours in. The game is so dam fun.
Another great one is Osu
- I was introduced to BAR like 3 months ago and I still have no idea wtf I'm doing.
  Online matches typically vary between these 3 experiences:
  Your teams seem evenly matched in skill, 3 people on each team still have no units to speak of 30 minutes in.
  One team has a true 20 openSkill player. They are consuming the other team's players whole at the 18 minute mark.
  It has been 3 hours, your's and your allies' units are a river flowing forth from your bases. They clash with the sea of enemies in a flurry of dazzling sounds. The frontline has held exactly at the middle for the past hour.
  
  It took me about 40 hours to go from Openskill 1 to os 2. I'm now os 5. I mainly play core front and just ball up tanks with a repairing station behind or I use my com to repair. Works great when it works but sometimes I get pushed before I have enough of a mass and then I'm useless and get crushed. It's definitely a chaotic game

CDDA probably. One of the more comprehensive zombie survival experiences
- What's the full title?
  
  Cataclysm dark days ahead
  
  Cataclysm: Dark Days Ahead. Zombie survival roguelike, forked from the original cataclysm by whales. Also check out Cataclysm: Bright Nights which is a fork of CDDA that makes it more gamey like the original, and less like you're playing 2d arma.
  
  Oh my bad, I forgot to put it in, looks like it's already got a reply though.
- My favorite thing is when I come back after a hiatus and my favorite strat's been nerfed and I get to struggle to survive like its my first time playing again. I remember when you could make a silent burst fire BB gun that shredded anything that didn't have armor, and mount them to your deathmobile en masse to just drive through cities untouched by the horde. The Radio Activated Noise Emitter + Caltrops strat's still good as ever, though the crafting requirements are a lot more complex since the last time I played.

Apart some of the already mentioned (mindustry, 0ad, beyond all reasons, zero-k), also minetest (minecraft), destination sol.
l've tried hege wars (worms clone) but found it meh. Sometimes supertux.
- Lately the modding has been getting really good, and while the game engine already has volumetric lighting (or something), there are even mods now that render everything beautifully that probably need a really good graphics card to keep up with.
- I had the same experience with Hedgewars, but I can't really say why it doesn't click like Worms for me.

Xonotic

Nethack. I remember playing it at university 30 years ago when it was text only. Amazingly, there is a version available for android and its fucking addictive.

Nethack.

Super Tux and Super Tux Kart

0AD, so good
- For those who don’t know: It’s basically an Age of Empires clone.

Not enough shout outs for Super Tux Kart soccer mode. Getting a group of friends playing that is awesome
- That, or the tire arena mode thing. Both are pretty fun when you are bored of all the official tracks and your favorite add-on tracks.
  
  Wait there's addon tracks?!
- True.
  Also, a single keyboard can be used to setup the controls of both user 1 and 2.
  Was awesome to play games together, without needing a separate computer or input device.

One of my favorites recently has been playing MineClone2 with some extra mods (can't remember which) through Minetest.
I've been boycotting minecraft since the news of chat reporting potentially coming to Java and MineClone2 is such a good replacement. Biggest gripe I have is not being able to get any of the mods that add sprint to work. Pretty much the only feature not available in MineClone2 (as far as I'm aware) from minecraft that I actively miss.
- Mineclone2 has sprint since the "sprint update" long ago. You get it by pressing "E" (or the "use" key if you remapped it)
  
  I'll definitely have to look into that! That is an absolute game changer that will definitely make the game a lot more bearable for me.
  Thanks for the info! I would have never figured that out on my own.
  Edit:
  Found it in the package manager. I definitely have that selective male blindness where I can look right at something and it won't appear in my vision.
- Is there any mod you know for making the world larger/infinite?
  I was a big fan of just traveling in Minecraft and finding new areas along the way. But minetest space constrains seems not to fit that playstyle unless there's a mod I don't know of.
  
  Have no clue. I don't even know how far out MC2 allows you to go because I've never gone to the edges of the world before. Only thing I know about world limits is that you can go thousands of blocks down in just the base game Minetest comes with, which doesn't apply to MC2.
  
  idk about mineclone, but in minetest the world size is limited to a cube that is 62k in any direction, or from the center 31000 blocks in any direction. Which may not sound like a lot but even in my techmc world on javamc i've only ever been about 10000 blocks out from spawn, and that's a multi minute commute in the nether (8x faster than overworld) even.
  Unless you are literally kurtjmac the likelihood that you will go that far is very small.
- i havent done anything with mineclone, but have messed with minetest, it's pretty cool. Whats mineclone like?
  
  Mineclone2 is pretty much a clone of Minecraft, like the name implies. It doesn't have all the current features Minecraft has, but it tries to make itself appear like a clone by having the same features as the official game. It works good enough as a clone. Also, someone here once told me they added sprint in an old update, but I can't get it to work if they did add it. So if you like sprinting around your world like I do, you might be out of luck.
  In general it has the same things Minecraft has, but they're plenty of updates behind the official game because (if I recall correctly) I'm pretty sure the people behind it want to make sure everything works before updating the game. Don't recall if that's true, so take it with a grain of salt.
  I'd have to check about looking into which features they have since it's been a while since I went into creative to check what they've added. I at least know they have the nether and end since there are achievements for them. Don't know whether they have the end dragon fight, so going to the end might be a bust for anything besides end stone.

I play DDay Normandy, a quake 2 mod
OpenRA d2k
Minetest
Veloren
Fun games

More recently, I'm a fan of shapez (shapez.io) for my recommended daily allowance of factory building gaming.
Going back further, I have a soft spot for Ri-li, a nice little game about toy trains with very charming music! It was this which set me on an adventure with the mod tracking scene. A surprising amount of open source games use them, it feels like open source music!
Reminded me also of Alex the Allegator 4, a very original 2D platformer
- Is Shapez open source?
  
  Yes - https://github.com/tobspr-games/shapez.io Though it's also on Steam for a small price to support the developers

Doom, or, gzdoom! You can use it to play the original Doom 1 and 2 games with modern mouse and keyboard controls on HD displays. And there's an endless number of fan made level packs to try.
As for open source AND free / open resources, there's Freedoom 1 and 2. I occasionally play them, they're fun, but a little lacking in stage design.

I like Ltris, Gweled, and Frozen-Bubble. I like simple games. I wish there was a good pacman for Linux too.
- Have you considered emulating the original ones?
  
  Yeah, I have had in the past, but it's a pain to find roms with the right version of mame. At least that's how it was back in the day.

mindustry. I've kinda quit playing games. But still play mindustry on my ipad. :)

Open RCT 2

I like Simutrans, which is basically an OpenTTD competitor with more complexity but an uglier interface. Sadly development on it has been fairly slow, at one point there was a one-way road patch but it’s since been abandoned.
- an uglier interface than openttd?
  
  I haven’t played OpenTTD, but comparing from the videos I’ve seen, yes it’s uglier.

What! Mindustry is open source!? Makes me love it even more

Sauerbraten

minetest is pretty cool. Highly decentralized which is nice. Very flexible, it's just a game engine essentially.
- Kiddos love Minetest; we've changed out mods a few times now to experience new combinations including some minor customizations to tweak difficulty a bit

Morrowind with vanilla OpenMW

Chess
- Thought about trying it, but it doesn't look like it's been updated in a while.
  
  There was a fork a while back which changed the board into hexagons but I don't think that fork has bee maintained for quite some time, and their build pipeline is hopelessly broken so you'll have to roll your sleeves up and compile your own from source with a lot of dependency chasing/substituting

Star Ruler 2, the company closed down and open sourced the game, it's a space 4X real time, has pretty good fleet combat and u can design ships, i think wasn't popular because the resource management and card system is a bit weird and harder to understand than other strategy games, but pretty fun after u get used to it...
- There's a community maintained fork, but i think it's missing some files (ship blueprints for some races)

Fellow Mindustry fan!
- I'd seen Mindustry before on Steam ... it looked interesting, but never "interesting enough". I decided to pick it up given all the love it's getting here :)

There are a lot of great responses on here! I've been playing (at least until my steam deck shit the bed two days ago) around with OpenRA and Minetest.

Nexuiz, or whatever they call it now after the original dev trademarked and sold the brand.
Edit: Xonotic is the name of the active fork.

Probably the Ur-Quan Masters.
- https://uqm-mods.sourceforge.net/Download
  An HD Remaster with optional QoL fixed and added content!
  One of the best games of all time.
  
  I'm a pretty big fan of Star Control: Origins, too.

Go / Baduk.
However the white stones are severely overpowered, and the devs refuse to do a rebalance since around the last 4000 years!
- But they have done a rebalance, several times. It's called Komi.
  
  Well, have you played recently? The white stones are still way overpowered! (I hope you notice the invisible sarcasm tag, alluding to the fact that stronger players usually play as white)

Veloren all the fucking way

Angband

Cataclysm: Dark Days Ahead

Shattered pixel Dungeon fancade and IDK if it counts but fightcade.

Space Station 14
- Oh dang, someone remade SS13? There goes next weekend.

I hate that Tales of Maj'Eyal is my favorite Open Source game. I hate that a new expansion is coming out soon and I will instantly buy it and play it and hate myself. Check it out!
OpenTTD and Widelands are also pretty cool.

For years I've played bzflag. It's a 3d tank battle game with a variety of play methods (capture the flag, soccer, -em-up, etc).
Other than this, there was once some kind of space opera with combat, politics, and other game functions. I can't remember the name now.
- Do you mean the Ur-Quan Masters? It recently released on Steam!
  
  No, but you brought back another memory! Star Control. I'm going to have to check it out. Thanks!
  I'm beginning to think the game i was wondering about is a fever dream.

I used to play Tremulous. That was a blast. Very clever game.
- That takes me back. Waiting on 1.2 release, any day now...
  
  I heard Unvanquished maybe scratches the same itch
- Whoa same! Always played on that server that had greatly increased the build points so there were turrets everywhere :D
  
  Oh yeah. I remember that. There was a nice consistent player base on that server

Neverball is a fantastic ball-in-a-maze (Monkey Ball) OSS game

These suggestions rock, I guess my weekend is set!

Xonotic is really fun if you enjoyed Quake 3 and Unreal. Has an active community as well. Beyond All Reason is a pretty polished RTS using Spring engine.

Mine would be Thrive, not so much due to its current gameplay, though it is okay, but moreso due to an unwavering commitment to a vision. It has gone on for years and is essentially a scientifically close to accurate version of spore. They have almost finished the single cell stage and are working some on the transition to multicellular now as I understand it. I find it to be an impressive project as it started from the disappointment with spore and has evolved into something that I would genuinely suggest as a learning tool in middle school biology class.

I played Warzone 2100 for a long time. It isn't as good as Total Annihilation (nothing is), but it had some interesting component-based units.
I should try Veloren some day. It seems very interesting.
- I played Warzone 2100 for a long time. It isn't as good as Total Annihilation (nothing is)
  Have you tried Beyond All Reason? It comes pretty close
  
  Yeah, I should.
- I found that game so difficult

Unciv

openarena?