You’re thinking of a Rectenna.

Edit: Ignore me, Admiral Patrick beat me to it.

Not federated but you can self host something like this. https://github.com/SillyTavern/SillyTavern

croc is a tool that allows any two computers to simply and securely transfer files and folders.

https://schollz.com/tinker/croc6/

• allows any two computers to transfer data (using a relay)
• provides end-to-end encryption (using PAKE)
• enables easy cross-platform transfers (Windows, Linux, Mac)
• allows multiple file transfers
• allows resuming transfers that are interrupted
• local server or port-forwarding not needed
• ipv6-first with ipv4 fallback
• can use proxy, like tor