Where the Source Filmmaker differs from most animation tools is that it acts as an all-in-one package for rendering, video editing, sound editing, motion capture, etc. So rather than rendering a 3D animation using one program and then editing the video in another, for example, an entire animated video can be constructed with just the Source Filmmaker. Don't be fooled by the apparent simplicity the program offers though; it's still a very complex tool with a steep learning curve.
http://www.gizmag.com/valve-source-filmmaker/23180/
this video is a 4 minute introduction to the features and potential
http://www.youtube.com/watch?v=Zri1c_If6Ic
there are a series of tutorial video if you wanna go full nerd on this then check out the homepage at
http://sourcefilmmaker.com/
yes, it's sort of Machinima, kind-of. But watch that intro video, it's also allowing Pixar level animation and control of character and editing ... for free.
