The popular mod that allows you to manipulate the physics in Half-Life 2, Garry’s Mod, plans on going retail through Steam. It’ll cost $10, and the profits will be split between Garry and his team, and Valve. The current version, 9.04 will remain free, while the upcoming 9.1 version will become the official paid release.
Supposedly the retail version will feature less bugs, and more updates. There’s no telling how well it will go over, I think it will largely depend on how much is added with the retail release to substantiate a purchase over the free version. So far the reaction has largely been negative.

