Kingdoms of Kalamar
Kingdoms of Kalamar is a Dungeons & Dragons campaign setting created by Kenzer & Co, probably more famous in /tg/ circles for their Knights of the Dinner Table comedic gaming comic and their HackMaster game. Originally taking the form of two books published for Advanced Dungeons & Dragons 2e, Sourcebook of the Sovereign Lands and Mythos of the Divine and Worldly, it was converted into a 3rd edition setting in the year 2000, and even had a brief 4th edition update. It's also the core setting for HackMaster from 2nd edition onwards.
Taking place on the continent of Tellene, on a world so primitive that its natives believe there is no other land apart from it, Kingdoms of Kalamar is best defined as a Low Fantasy Medieval RPG; casters are rare, most NPCs are low level, PCs are the only "true" heroes in the land, magical monsters are rarer than in, say, Forgotten Realms, and the general tech level is Late Iron Age at best. The titular Kalamar Empire, long the dominant power over the world, is fracturing, resulting in a time of great upheaval as different provinces exert their independence, and foreign empires seek to take advantage of this. Rather than separate pantheons for each race, the gods of Kalamar are simply worshipped in different names and preferences by different cultures
Interestingly, humans feature very prominently in the setting, having six varied subraces which have their own cultures, languages, and aesthetics.
Also, hobgoblins are the dominant evil humanoid race, with a pair of mighty and somewhat Asiatic-themed empires, and orcs are feral tribes in the wastelands considered more a persistent nuisance with regular raids on civilized lands than a people. Besides those mentioned, Elves have three very small and distinct kingdoms, and dwarves, gnomes, and halflings are mostly downtrodden.
The downside is that KoK can take its "low fantasy" focus a bit too far. Although its defenders argue that it's a "story game", this is one of the only D&D settings where an official adventure includes the PCs being assistant farmers. No, not in the traditional "pesky varmints are stealing my livestock and stuff - kill them for me!" sense, in the sense of helping to sow seeds and harvest crops. Adding to this, KoK's writers took an unusual approach to mechanically balancing things. They placed much emphasis on martial skill in a game where, as we all know, wizards always ultimately grow much more powerful - ironically, some of their special native races, such as Golden Halflings actually gain bonuses to multiple mental stats and penalties to physical stats, while Half-Hobgoblins, do the opposite.
The 3rd edition Kingdoms of Kalamar books are notorious for being some of the worst content to be officially branded Dungeons & Dragon (not merely OGL, though it's a strong contender even in that) since they somehow got WotC to officially license it.