Friendica – A Decentralized Social Network
Friendica – A Decentralized Social Network
You could use this: https://github.com/Qbix/Platform
Example: https://freecities.app
Video demos: https://vimeo.com/1141492621/23e8b84b8b
Disclaimer: I built it. Lovingly, over 15+ years.

Free, open-source community platform, decentralized alternative to Big Tech. For apps that empower people and unite communities. - Qbix/Platform
If you also want to host or build interesting social apps, you should definitely do an isolated atproto / Bluesky service!
https://blueskydirectory.com/
As for actually doing this... running a PDS and relay isn't that hard, and the red dwarf web client is online and can be configured to point to whatever appview you want. There's significantly less experience running your own appview, but there are options & folks are happy to help.