- Family Sharing: http://steamcommunity.com/groups/familysharing (in case you've been living under a rock)
- In-Home Streaming: http://steamcommunity.com/groups/homestream
- Steam Music: http://steamcommunity.com/groups/steammusic
In-Home streaming is a great solution to me moving my computer all around the house. Instead i'm currently looking around for a really cheap and small computer that can handle streaming to it, i'm already in the beta as well.
Haven't really made up my mind about Steam Music. Nothing revolutionary but might come in handy and eliminate the need to Alt-Tab to pause/play/change volume when i'm in-game.
You can but you don't have to get a beta invite for all of these if you join these groups on steam.