Tekumel is the RPG world with the longest history of publication. It started in about 1975, and has been in and out of print ever since. The latest incarnation is the version from Guardians of Order.
The background draws a lot to the large, densely-populated empires of India, Mesoamerica and South-east Asia. Society is rigidly statified, honour and respect are paramount, tradition is vital and baroque. It's a fascinating and alien place. For more, see the Tekumel homepage.
The GoO game is based on Tri-Stat, and is rather crunchy in places. There is enormous scope for customisation of characters in the rules, and this seems to be expected to be used in play.