Valve has released an update to its Source SDK offering support to Mac and Linux developers.
As part of the new update, source code for the development kit will now be hosted on Github.
A new licence is also available that allows developers to make changes to the SDK more easily.
The SDK launcher itself is now set to be phased out, and will soon be taken off the Tools list, with the Hammer editor and other mod tools to come alongside their related games.
Other changes and additions include SDK support for virtual reality headset Oculus Rift and dedicated server support on Windows and Linux.
For more information on the Source SDK 2013, visit the official website.
You can also access the source code on Github here.