On mastodon there is sunbeam.city that was inspired by social coop.
Outside mastodon theres a few platforms run by cooperatives of user/owners. #platformcoop
Plus there are #coops which have set up platforms for use of their members, but where the #coops purpose isnt the platform.
eg. https://community.coops.tech/ - its also open to people who are not in the member coops (its a coop of coops). So for them coops.tech is a benevolent dictator.
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko