As promised, Valve has released the first test release of SteamOS. From the FAQ:
SteamOS is a fork (derivative) of Debian GNU/Linux. The first version (SteamOS 1.0) is called 'alchemist' and it is based on the Debian 'wheezy' (stable 7.1) distribution.
The major changes made in SteamOS are:
- Backported eglibc 2.17 from Debian testing
- Added various third-party drivers and updated graphics stack (Intel and AMD graphics support still being worked on)
- Updated kernel tracking the 3.10 longterm branch (currently 3.10.11)
- Custom graphics compositor designed to provide a seamless transition between Steam, its games and the SteamOS system overlay
- Configured to auto-update from the Valve SteamOS repositories
You need to have an NVIDIA card for it to work, since Intel and AMD graphics are currently not yet supported (work is underway).