Attention current and would-be mode developers: Valve's free Source SDK has been updated with a swag of new features.
The headline change to this year's version of the Source SDK is the addition of native Linux, Mac and Oculus Rift support, allowing for quick and easy cross-platform developerment as well as VR compatibility.
As detailed in the release announcement, the Source SDK is changing the way it handles tools. You'll now find Hammer and the like bundled with individual Source Engine games, and the SDK launcher will be phased out.
Modders will be able to add Steampipe support to their work, and set up dedicated servers for PC and Linux.
It's worth noting that the SDK's license has changed, too, so it's easier to share your customisations; read all about that here.