Valve is releasing the Source Filmmaker (SFM), the movie-making tool Valve uses to make movies inside the Source game engine. SFM has been used in quite a number of Valve trailers. SFM is currently available in beta. To apply, simply visit the official website with a computer that already has Steam installed on it. "Initially, we are limiting the number of beta users, but soon we will release the SFM to all users on Steam for free," Valve's FAQ explains. At launch, SFM will only work within Team Fortress 2, meaning fan-made Half-Life movies using SFM won't be possible for a while. However, Valve notes that "users familiar with modding with the Source engine will be able to mod the SFM build of TF2 to create new worlds."

If you're interested, here's what you'll need for Filmmaker:

-OS: Windows 7 / Vista (Windows 7 64 bit suggested)
-Processor: 3.0 GHz P4, Dual Core 2.0 (or higher) or AMD64X2 (or higher)
-Memory: 2GB (4 GB suggested)
-Hard Disk Space: At least 15 GB of Space
-Video: NVIDIA GeForce 200 series card or better, or AMD Radeon 3000 series or better (NVIDIA GeForce 400 series or AMD Radeon 5000 series preferred)
-Monitor: 1366 x 768 (1920 x 1080 suggested)
-Audio: DirectX 9.0c compatible
-USB headset with mic (suggested)

As a small bonus we finally get to "Meet the Pyro"!