Epic has kindly released their Unreal Engine Development Kit (UDK) for free (this is the part where all you aspiring video game developers get excited like little girls at a Jonas Brothers concert while they cover a Twilight song).  I am not clear whether it is all the tools or most of them but it doesn’t seem like they watered it down too much. Of course it is free so it is for noncommercial use only. You can acquire the right to sell your game or use it for some other reasons by purchasing a licence.

This is a great tool to use to introduce and educate yourself in video game development. Epic is offering tools and tutorials for users to learn how to use the engine.

Oh and it comes with a demo of Unreal Tournament 3

Download and info here