Opera browser used to have P2P file transfers as a short lived feature in ~2010, called Unite. I remember it also had skeuomorphic GUI of a 'fridge' where users could put post-it style notes that could be seen by others.

One of many everything-and-the-kitchen-sink features Opera Presto had during its heyday. Others included a separate Bittorrent client, desktop widgets that could be moved outside of the browser window, full IRC client, email client and peerless hotkey actions customization.

By some miracle the browser still managed to be a rather lean binary.