Valve's source filmmaker has been released to the public. This tool allows the user to create and edit videos with the source 3D engine.
This release is a working beta. Valve has opened a steam community where SFM users can share their videos here. Valve is also going to release the "Meet the Engineer" episode in addition to the "Meet the Heavy" for people to edit.
The source filmmaker can be downloaded on Steam.
source: http://www.sourcefilmmaker.com/