For people and teams developing mods and games with Valve's Source engine.
Gabe Newell: "We’re spending more time on tools development now than anything else."
The TF2 team have opened a new web page, where you can upload your hat and weapon models for inclusion in the game as unlockables.
FaceAPI can track a user's facial features via a standard webcam and immediately map them onto a virtual character.
Released, that is, but barely usable. All the same: launch with -tools to access them.