The Leadwerks Game Engine game launcher now works with SteamOS with a few caveats. From the Leadwerks blog:
Leadwerks Game Launcher now works with SteamOS, with some caveats.
First, you must set the application to use the "Official Bindings" controller configuration by Leadwerks Software.
When you start Leadwerks Game Launcher on SteamOS, a page of available games will be shown. Click on the game you want to play. The game will be shown on a new page, and a blue button will appear on the bottom left of the screen. You can press the B button on your controller to go back to the main page, or mouse the cursor over the blue button and click (right trigger).
The application will pause while the game is downloaded. At this time no progress indicator is shown while downloading, but most games only take a few seconds. The game will then launch. Most games can be exited by pressing the right arrow button just to the right of the Steam button on your controller. Some games will presently not work correctly.
To exit the game launcher, press the right arrow button just to the right of the Steam button.