For a long time now, Valve has wanted to put Steam on open source operating system Linux.
Valve's first mission was to get zombie-shooter Left 4 Dead 2 ported over to Linux-based OS Ubuntu. Now that's been done, Valve are looking to optimise the port.
On their Linux-themed blog, Valve laid down their objectives: "Getting the Steam client onto Linux with full functionality, optimizing a version of L4D2 running at a high frame rate with OpenGL, porting additional Valve titles."
Valve's goal is "a fully-featured Steam client running on Ubuntu 12.04," and they're not far from achieving it. They want to have "L4D2 performing under Linux as well as it performs under Windows."