I have thought long and hard about "Free" licenses and I think there are few types of licenses (these apply obviously to source code)

Free for Anything license - Somone can take your code, compile it and sell it, and you are cool with that. (They can even say they made the game themselves)
Free for Use - Someone can take your code, modify it a little to fit their game and sell it and you are cool with that.
Free for Learning - this is the sort of license that says you can use the ideas and make you own similar game, but you cant sell my game.

None of these are official license types, just the types I made up when trying to define how my freeware programs would be released.

Any game of mine that includes a source code release is released as Free for Anything. (Games I want to selel I do not release the source)