Steam Linux. Steam added more than 30 games that run on Linux, spanning standard releases and a few Greenlight games, and Steam Linux is currently in closed beta.
We attempted to find the Linux system requirements on a PC and via a virtual box running the latest version of Ubuntu, but to no avail. A few faster people snapped screenshots of the specs, such as the above image of Serious Sam 3: BFE's Linux requirements taken by Techgage.
Yesterday's discussion of a Steam Box, direct from the mouth of Valve founder Gabe Newell, raised questions of Linux as a potentially pivotal player in Valve's arsenal. That thing will have to have an OS, after all, and Linux would be a natural option. As we discussed on the Super Joystiq Podcast last week, Big Picture mode plus Linux might equal a big ol' Steam Box.