Certainly not as powerful as common office suites, but https://cryptpad.fr/ is not only open-source but also has already running instance (and has end to end encryption for your documents)
https://syncthing.net/ is a good general file synchronizer. Requires devices too be online simultaneously to sync, but gives you transport encryption with forward secrecy.
I’m fairly sure I’ve seen an NNTP based imageboard that distributed it’s content through that protocol and different instances had overlap of boards. That’s about the closest match to federated system you’re going to find with this model I think. Interesting concept. Not something I’d want to interact with personally though.