Copyleft?

http://www.gnu.org/copyleft/copyleft.html

I find it rather frustrating when people arguing for greater freedom decide to be just as restrictive regarding distribution of their software as those arguing for control. Ultimately, both systems produce software that is useless to many businesses and entrepreneurs. If I want to make a game with the intent to sell it, I need software I'm allowed to sell, not something restricted to being used in free works. Such restrictions greatly hamper the spread of software tools, slowing down progress. (Copyright restricts distribution to owner permitted methods, Copyleft restricts distribution to free methods).

I much prefer the WTFPL.
If you intend to sell it, use copyright. Otherwise, just put it out there for all to use, so it can spread as far as possible. Copyleft is just another way of using copyright to set rules on how software and other works can be used.

P.S. Copyright laws in general need to be heavily reworked.