Garry's Mod, for those not in the know, enables you to create scenes using game worlds - usually Half-Life 2 - with the models and game objects becoming your props and actors.
"The new version has been created from scratch so almost everything has been revised and re-invented," said mod author Garry Newman. "It has a bunch of new tools to play with (winches, hydraulics and hoverballs), totally new spawn menu and a few new Post Processing effects to play with. The great thing about Steam is that I can update really regularly, really easily - which is something I plan on doing - so expect more tools/gamemodes/stuff to come."
The Steam version will be available from November 29, and will cost $9.95 for those of you who already own a Source-based title such as Half-Life 2. There's also a bundle that includes a copy of Counter-Strike Source, which will set you back $24.95.