Valve updated its free software dev tool Source SDK to support Mac OSX, Linux, and the Oculus Rift. Clients can be built and run in Windows, OSX, and Linux in Source SDK 2013, and dedicated servers can be run on Windows and Linux. As for the Oculus Rift, Source SDK 2013 can provide VR support via a compatible mod, enabling stereo and head tracking.
Users can find the Source SDK 2013 code at dev project hosting service github now, while a new license agreement means mod makers can share their work "more easily." Also, the Hammer editor and other mod tools come with games rather than the SDK launcher, which Valve said is being phased out.