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.
Slidematch is a media rating, contextual retrieval, peer recommendation, and library management system for music, video, movie, and book impressions. It adds value to your existing media player by enabling you to easily record detailed impressions, retrieve content appropriate to what you are currently doing, and interact with friends.