misskey!
Why isn't it so popular compared to mastodon? I just found out about it and it looks pretty mature imo, it's only popular with japanese people.
It just doesn't seem very aimed at Westerners. There is a mature fork gaining prominence that is called Calckey… at least, for the next 5 days, until it rebrands. I suggest you check it out.
Misskey/Calckey look really interesting. The main reason I haven't (yet) switched over from Mastodon is the worse support from third-party apps.
Third party apps can change the interface/appearance of Mastodon, so what advantages do Misskey/Clackey have over Mastodon?