For anyone interested, I'm making an open source clone of reddit that is federated using activityPub. Everybody can host it's own server and each server can talk to eachother so you can interact with threads and comment from other servers.
The project is in very early stage, but it's usable and lind of cute.
The other one similar that I know of is prismo. If they all use activityPub they will be compatible. They will also be compatible with mastodon (which is like twitter), peertube (which is like youtube) and many others.
The project is in very early stage, but it's usable and lind of cute.
https://moontreeproject.org