The beta supports free-to-play shooter Team Fortress 2, as well as about two dozen other Steam titles. The beta also includes the online store's Big Picture mode, which makes using the system easier on a TV with a controller.
"This is a huge milestone in the development of PC gaming," according to Gabe Newell, Valve President and co-founder. "Steam users have been asking us to support gaming on Linux. We're happy to bring rich forms of entertainment and our community of users to this open, customer-friendly platform."
The beta is available for installation on Ubuntu 12.04, but additional "popular distros" are expected in the future, according to Frank Crockett, a member of the Steam for Linux team.
Valve received more than 60,000 responses to its request for participation within a week of announcing the Linux beta, according to the press release. The participants in this closed beta were pulled from that group with plans to expand the testing group over the course of the beta. Future participants will be selected from survey respondents.
Once the beta is stable, the Steam for Linux client will become available to all users of Steam, according to the release.