I knew about for at least a few years but I was afraid that the clients would be unpolished. Now that I'm here, I must say I am pleasantly surprised by how good all Mastodon apps are. Both Android and iOS apps are easy to use and reasonably smooth. Though I don't use the web UI much, it's pretty good as well.

types.pl

A Mastodon instance for programming language theorists and mathematicians. Or just anyone who wants to hang out.