Hear me out: a fully fledged desktop environment, like KDE Plasma or Gnome, but it's a 3D world - "windows" are just walls, the file explorer is just a bunch of procedurally generated condos, and you get a Gmod physics gun to move stuff around.
Making your own engine is worthwhile learning experience. The same as trying to recreate any of the foundational tools that you use. Might not be the fastest or best way to make a game but a good way to make yourself a better developer.
This is my 4th Vulkan related "project" and 2nd attempt at making something other than a glorified tutorial workspace in 6 years, and it took me 4 weeks to draw this stuff with minimal technical debt.
I could just use an existing game engine, but what's the fun in not manually sorting all draw commands by mesh>pipeline>material and hunting synchronization hazards by just looking at funny glyphs for extended periods of time?
Keep in mind that if you actually want to make a game, make a game not an engine. Too many video game projects get bogged down in the engine development stage and never make it to completion.
Do people even make their own engines anymore? If this wasn't a pet project I would have dropped the entire thing as soon as I started dealing with 3D models, and visited Godot's homepage.
...
Perhaps I should get my hands on Godot at some point.