What non-4e would you play if there was no OGL at all?
Previous edition of DnD with used books
The thing is, that such OGL games do exist solely because the guy who first wrote the d20 OGL license, didn't do his job very well. He left a bad-wording / loophole that let publishers use the OGL to write their own independent systems that can now exist on their own without any concern for GSL and such. However, if the original lawyer had done his job properly, there wouldn't be any True20, C&C, Pathfinder, etc. available.