Wilderlands
Has hints of "old" technology. What is that technology? Whatever you want it to be.
They have a large variety of races, including hawk people, and many others, that you can use, totally ignore, or decide to use later on.
There are a lot of "hidden" history and elements to the Wilderlands. Such as ancient ruins of a god, with these ruins beings its last link to the Wilderlands. So PC's can finally destroy said deity, or work to bring the religion back to prominence.
There are thousands of gods, from world spanning religions, to a single settlement, or the aforementioned "lost ruins".
Basically, I see the Wilderlands as a very fluid world with whatever I want to be there be able to be inserted. Greyhawk, FR, and many other worlds have to fixed, and too detailed, of a history.
Wilderlands give me enough structure to run as it is, but to "homebrew" whatever I want, whenever I feel the need. After all, the "official" mapped area are the size of the mediteranean region of the real Earth. So I have a huge unknown world surrounding a not so well known area, to do whatever I want with.