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.