Valve's Source Filmmaker is now in open beta for everyone. The storytelling tool lets fans have full control over creating animated movies set in the Team Fortress 2 universe. Just head on over to the Source Filmmaker website, and click "Install SFM. It's FREE." on the right hand side to get access.
There's already been a number of insane videos made by the Valve community. I'm looking forward to seeing the flood of new content now that this is open to the public.