I use firefish (formerly calckey) as a sort of alternate to mastodon. It's a fork of misskey (forked a couple of years ago I think).
And yea, it's a nice alternative to mastodon, not least because you'll be able to interact with mastodon people just fine, and will have more features than them not fewer.
The main thing its got going for it is a nicer/better/richer UI with longer comments as default.
It also has a lot more actual features (like search, channels, pages, grouped bookmarks, markdown that allows animation and antennas for creating feed from filters). But in the end, having poked around it a bit, many of these features require polish before they're true selling points in comparison to markdown.
The selling points that apply now are the UI or interface, the emoji reactions, richer markdown support (where mastodon has none, WTF, it's 2023!), longer post lengths, and actual threading of conversations! You could also add that mastodon is too dominant and platform diversity needs to be supported.