The Source Engine is kind of a big deal. It's been around since Half Life 2, has been the stable backbone behind Valve's games, and has been relatively open for modding and experimentation. Well, if files hidden in the newly released Source Filmmaker are to be believed, it's getting a sequel. ComputerAndVideoGames Here's the Valve Time thread if you'd like to see exactly what these guys have uncovered. Recently when talking about the Steam Engine, they guys at Valve said they, "...don't like to brag, but Source is considered the most flexible, comprehensive, and powerful game development environment out there. And it's about to get even better."