Valve has just released a beta version of the Authoring Tools for Portal 2, which features much of the tool set used by Valve itself to craft the environments players encounter in the full game.
The Authoring Tools allow for the custom creation of everything from single-player and co-operative test chambers, character skins, 3D models, sound effects and even music.
The tools can be downloaded now by anyone who owns the PC version of Portal 2 by clicking the "Tools" tab in their Steam client.
While the Authoring Tools are strictly PC only, Valve contends that some of the user-made creations will eventually see the light of day on the Xbox 360, PlayStation 3 and Mac platforms.
Find out more at the official Portal 2 blog.