updated 04:35 pm EST, Tue January 31, 2012
Invites no longer equired
After a brief period of exclusivity, Valve has opened up the Steam Mobile beta to the general public. Previously just a select group of Steam users were allowed to try the beta, although invites handed out to testers gradually increased the userbase. Free Android and iPhone versions of the mobile client are available.
While people can't actually play games using Steam Mobile, they can keep track of friends on Steam, chat with them, and access news, groups, and user profiles. The apps also allow buying games, which can be downloaded once a person is back at a Mac or Windows PC.