Using the L4D Authoring Tools, you can create your own campaign maps, character skins, 3D models, sound effects, and music and load them into the game.
Here's what's included:
- Updated version of Hammer, the source level editor
- Updated suite of command line compiling utilities
- Updated Particle editor
- Updated Faceposer
- Example maps, common infected, props, and explosives
Thanks go to Thomas Wenzler for sending this in and the source via http://news.sketchucation.com/