robonobo is social music sharing and downloading software. It allows you to share your friends' music libraries and playlists, stream the audio instantly, and download the file in the background so you can burn it, export it to your music player, or do whatever you want with it. You can import your friends list and share links to your playlists via Facebook and Twitter.
Proximate is a social peer-to-peer (P2P) application designed for local device to device networking. It provides social communities with several user functions: Messaging, file sharing, and message boards. The application is designed to be completely P2P, i.e. servers are not needed. It only assumes TCP/IP networking, which means that it works over wireless/wired links such as ad hoc WLAN and Ethernet LAN. The application is written in Python for GNU/Linux systems with a GTK+ GUI, Nokia N900 being the primary platform.