Forgive my ramblings, but here's the main differences I see, from a community perspective:
Bluesky's for people who loved twitter circa 2015
Mastodon's for people who loved the format but hated the way the platform made use of it. The community is FOSS-focused and anti-corporate.
Bluesky folks are anti-corporate, but they still want their social media to be on a single platform and tend to dislike federation
Mastodon folks tend to be in smaller circles and more tech enthused
Features-wise, Mastodon kills the algorithm in favour of chronological timelines and lists, while Bluesky embraces algorithms, allowing people to even make their own algorithms for the platform. Bluesky's AT Proto uses "DIDs" to identify users, which are associated directly with a domain^[or subdomain]. This means that when federation does eventually happen, usernames will just be @my.domain.com instead of ActivityPub's @actor@my.domain.com.
Federation's still not enabled so I have no clue how things will look and feel on that front, nor am I familiar enough with the protocol to make any claim about how versatile it is. ActivityPub is flexible enough to be a Twitter clone, a reddit clone, a blogging platform, a youtube clone, a twitch clone, a goodreads clone, or several other formats. AT Proto's currently only proven to work for a Twitter clone.
You can just click Follow and start following someone. You don’t have to perform a copy-paste dance to bring the username back to your instance and do the following there.
A place where normies can feel at home, knowing that they won’t feel out of place not having a fursona or favourite Linux distribution and won’t be scolded for not using alt text or some inadvertent picoaggression. Also, the promise of clout.
Not a lot. Simpler signup flow and ecosystem, more twitter-like timeline and features, better discoverability and some communities that aren’t on Mastodon. FOSS diehards can mince about it all they want and blame idiot users, but the simple fact is people who don't live and breathe technology still have lots to offer a social network, and Mastodon continues to alienate them in design and in community. Lemmy does too.
I like Mastodon and Lemmy, a lot. I prefer them to the alternatives. But I just signed up for BlueSky and I’m enjoying it a lot even routed through the Mastodon bridge, simply because there are more diverse communities there, whereas my Mastodon feed is 90% tech and dev people despite spending hours and hours hunting for people I used to follow on Twitter. Getting big App.net flashbacks.
I like Mastodon and the Fediverse, I really do, but I just can't deny that all the good posters that made Twitter enjoyable moved to Bluesky. My Mastodon feed is nothing but journalists, activists, developers, but very little fun shitposting.
Easier sign up. On BlueSky you can just sign up for an account and go. You don't have to worry about picking an instance or anything like on Mastodon, which can be a bit off-putting for someone not familiar with federation.
Bluesky is to Mastodon & ActivityPub, what Matrix is to XMPP/IRC... a completely over-engineered system, ignoring all well established international standards and run by a for-profit entity with venture capital funding.
Feeds/timelines are first-class citizens in the AT protocol and are decoupled from account hosting.
On Mastodon, your timelines are computed by the same server that hosts your data. Consequently, signing up to a server to have an account on the fediverse is the same thing as joining a community. You follow the servers rules and share the same local timeline as everyone else on that server.
On Bluesky, feeds are arbitrary, fungible and provided by any server, and it can be computed/curated/moderated however they like. So communities are "built" around feeds rather than around account hosting providers.
The AT protocol also has "real" account portability (though I have not seen this demonstrated in practice https://atproto.com/guides/overview#account-portability). On Mastodon, account "portability" is a delicate dance that requires the cooperation of both the origin and destination server.
Mastodon has something that Bluesky currently doesn't: real federation. The Bluesky server that everyone signs up to doesn't federate with anyone else, since the whole protocol is still a work-in-progress.
Tho I agree with all the comments I have to say the general vibe of bluesky is more playful and fun compared to mastadon, perhaps its just my bias. But just like lemmy generally feels like a nice place to be so does bluesky- the vibe feels inviting.
I hate gatekeeping so much, but what I'm about to say is going to contradict that statement so much I should probably stop typing and start this post again....
Anywhoo....
If a troglodyte can't figure out how to sign up for the fediverse, then they should stick to CorpoChat
I think emulating twitter was a huge mistake for mastadon, the twitter reply structure that makes it difficult to have a long conversation with multiple people to be the main part of the post but ideal for "dunks" and outrage farming. I think the Tumblr reblog structure would have been an infinitly better choice for the more actual socialising thing fediverse is going for and a small user base that isnt producing much content and can re-circulate older posts. also it's less image-centric allowing more posts to be stored on a server, additionally (intuitively, I haven't thought about implementation that hard) it seems like a much more natural fit for federation.
If you go on Bluesky they will tell you. Lots of people saying that they feel isolated because there is no algorithm feeding engagement, and federation doesn't lend itself to finding your friends from Twitter easily without one of those migration tools people were using. Then another chunk describe Mastodon users as a "HOA" because someone told them to put a CW on something.
Portable accounts and being able to add third party layers to your feed for moderation and sorting algorithms. At least that's their design goal, idk if it's actually implemented because I never got an invite after like half a year.
Main positive thing I’ve heard is that it has a different vibe and culture that some might find more open and fun and sometimes even less problematic. That’s just hearsay, I’m not on there, but I’ve heard it from people I like and trust (on masto).
People are happy to peddle incorrect information which is easy to find. Dorsey is on the board, but deleted his account and used Nostr and Twitter significantly more than he ever did bluesky.
Cultural debt: Mastodon has the cultural debt of reply guys, FOSS bros, racism etc During the great migration a lot of minorities attempted the switch and were met with a lot of racism which was easy to hide due to PM. Mastodon also has the onboarding issues.
Studies show most users are passive users of social media, they don’t want much friction just to lurk.
Bluesky appealed to minorities particularly Black women very early in the process and that contributed to the growth and culture. They’ve lost some of the goodwill due to some moderation issues. But, without the cultural debt and without making decisions such as no full-text search (since changed) and no QTs, two features that benefits minorities and professionals alike turned off many.
There’s also no current federation so the onboarding is simple and smooth.
The culture on Mastodon based on 4 polls I’ve seen with 10k plus responses, Mastodon leans older than bluesky.
Unlike what’s put out there bluesky doesn’t aim to be a Twitter replacement but more so Mastodon+.
Lastly, the culture on Mastodon often takes itself too seriously while bluesky is mostly horny, crapposting, awareness raising and lots of laughs
They have the main thing masses often look for: unity (as in the state of being united, not the company). Like it or not, federation is a brand new concept that regular users can't wrap their heads around.