I think you'd find Pleroma interesting, it has old Twitter vibes but Mastodon is way fuller by far. But it's interoperable with any Fediverse platfotm, this is an invite-only instance ran by one of the devs post.ebin.club, other two but public ones:

• udongein.xyz
• stereophonic.space

Or check a list of servers/instances by one of the following:

• the-federation.info
• fedidb.org
• pleroma.fediverse.observer

Also: community list of Fediverse mobile apps including for Pleroma, both for iOS and Android.