mastodon/docs/Using-Mastodon/List-of-Mastodon-instances.md

List of Known Mastodon instances

Name	Theme/Notes, if applicable	Open Registrations
mastodon.social	Flagship, quick updates	Yes
awoo.space	Intentionally moderated, only federates with mastodon.social	Yes
social.tchncs.de	N/A	Yes
animalliberation.social	Animal Rights	Yes
socially.constructed.space	Single user	No
epiktistes.com	N/A	Yes
on.vu	Appears defunct	No
gay.crime.team	N/A	Yes(?)
gnusocial.me	Yes, it's a mastodon instance now	Yes

Let me know if you start running one so I can add it to the list! (Alternatively, add it yourself as a pull request).