Had never heard of #RetroShare, sounds interesting.
For #FileSharing alone, the CLI tool #MagicWormhole is simple and fun to use.
https://github.com/magic-wormhole
There are also some GUI frontends to it.
There's also #pairdrop if the other party is unwilling to install an app.
I guess most of the world simply shares files by attaching them to a #WhatsApp or #Telegram or #Signal message.
#Briar is a #p2p chat app with great potential, though I don't know its file sharing size limits.