In recent weeks, people unhappy with Mastodon project talked about forking the project in a different direction. It's harder than it looks.
A lot of people have talked about the possibility of forking Mastodon to get the many improvements their communities need. Making such an effort successful is another discussion entirely.
What did nextcloud fork?
The original project was called Owncloud and was made largely by the same people, but they split over a disagreement in management.
Nextcloud is a fork of Owncloud. IMO, as a product Nextcloud is superior in every way.
Owncloud