Reddit points out that the UNITY game development tool, is now free. There is some discussion on Reddit about it. Unity, which I've never heard of, is described as:

Unity is a multiplatform game development tool, designed from the start to ease creation. A fully integrated professional application, Unity just happens to contain the most powerful engine this side of a million dollars.

All that, cross platform (Mac, PC, iPhone, Web), and free. Wonder what the catch is?