The Source Filmmaker (SFM) is a software moviemaking tool built by Valve – the video game makers of Portal & Portal 2, 
Team Fortress 2 and “Meet the…??? short films. SFM gives users the ability to make animated movies by repurposing the video game world (the base game assets from Team Fortress 2 and “Meet the Team??? short films) into a virtual movie studio.
This is not for the novice user – but if you have experience in video editing and/or 3D animation you will hit the ground running with this incredible tool. There’s a Youtube channel full of tutorials that can be found here. Oh… did I mention that it’s FREE! All you need is a Steam account (also free) – then you can download SFM here.
Check out their introduction video that will explain it all (below):
