Mod makers rejoice: The Team Fortress 2 SDK has arrived! We've updated the Source SDK with all of TF2's client and server game code. Change, extend, or rewrite TF2, and publish them as mods on Steam. www.teamfortress.com/post.php?id=...

This is all following last year's 25th Anniversary of the original Half-Life, which we celebrated by updating the original 1998 game for modern systems, adding four new multiplayer maps, a documentary of its own, and much more: www.half-life.com/halflife/25th

Half-Life 2 turned 20 last weekend, and we're celebrating with a big update: New developer commentary by the original team, Steam Workshop support integrated into the game, Episodes One and Two are bundled into the main menu, and tons more: www.half-life.com/halflife2/20th