Imaro
Legend
I'm not familiar with the terms of their license (the trademark portion, not the OGL portion, presumably there is one since 3PP products seem to have the RQ logo on them). But that makes two if it's royalty-free.
Of course, Mongoose would likely not exist without WotC's OGL.
Here you go... Open Game Systems - RPGnetWiki .. sometimes I feel like enworld has tunnel vision when it comes to certain things, outside the realm of the d20 system.
* And while Mongoose may not have come into existence without WotC's OGL... they certainly are staying within the spirit of the old OGL, with their license, free magazine, etc.