One of the main issues people foresaw with SteamOS and Steam Machines is the relative lack of games on the Steam for Linux platform. Especially the big-name games that would be a draw for a lot of gamers. While the in-home streaming functionality can be considered a solution, it’s not the most practical one.
Perhaps with this in mind Valve has released the source code to ToGL, their Direct3D to OpenGL abstraction layer that’s being used in DOTA 2. It’s mainly for reference though, as it’s optimised for use with the Source Engine, however it’s one more step towards a more unified PC platform for video games.
You can have a look at the code now on GitHub, but be warned, there’s little to no documentation and no support will be provided by Valve.