We are just starting to integrate the SDK with our node-webkit based game greenheartgames.com/app/game-dev-tycoon (which was recently greenlit by Valve). At the moment I think it will simply be a nodejs plugin but I haven't looked into it in detail yet. We are NOT using C2 so I don't know how much use our integration will be but we do plan to open-source the integration part once we get it running.
The game "game-dev-tycoon" with steamworks api is online on steam. Any open source plan in the next weeks/months?