Bluesky is a different protocol than Mastodon, but conceptually I think it's fair to say they're similar.

I think Bluesky would clean up if it could also interop with Mastodon - people want to leave Twitter but it sucks having to choose between Mastodon and Bluesky and so I think some folks are just in a holding pattern waiting to see what wins. Bluesky feels more like Twitter so I think it would get a lot of folks, but I think people hesitate to bet on it just yet.

Bluesky has a 300 character limit, Mastodon has 500, non-Mastodon ActivityPub servers have a configurable limit. Mastodon can render markdown, has subject lines which are commonly used as content warning tags, can translate posts. It supports custom emoji and non-Mastodon ActivityPub servers support custom emoji reactions. Bluesky has more discovery features like community-curated lists and algorithmic suggestions of who to follow.

Mastodon features a more complex content filtering based on keywords [1],[2] and you can always try to pick instance that fits your needs. Hashtag support is here since beginning if I'm not mistaken. Bluesky has a rather simplified filtering [3], [4] that most likely will be appealing to mass users, tho since service revolves around customized multiple feeds they shouldn't in theory see and interact with the content they don't like in the first place [5]. There's no hashtag support so far - which seems odd because this is a pretty much standard feature on social networks.

[1] - https://ibb.co/km5nGDW

[2] - https://ibb.co/Xpp7t05

[3] - https://ibb.co/QcG1G4d

[4] - https://ibb.co/K2WPvfW

[5] - https://blueskyweb.xyz/blog/3-30-2023-algorithmic-choice

Mastodon uses ActivityPub for interoperability with a wide ecosystem of apps