Mmkay, I'm not sure how to tell if something's Open Game Content, but the book I'm looking at only has the WotC OGL information copied verbatim, and no extra mentions of content so I'm going to assume that means they consider the manuals OGL themselves. But the only not WotC book I actually used for anything I adore, so.
Mythic Vistas Egyptian Adventures Hamunaptra. Full Egyptian campaign setting with races, spells, and general awesomeness. 3rd edition, apparently part of a set involving Testamnt and the world of Freeport. I never saw any of the others to use them.
Edit: It's from Green Ronin.