I've done extensive work for running Dark Sun in the Forbidden Lands setting.
Lots of documents available at: https://1drv.ms/f/s!ArMRWhb_Dxr2iJMZp8MPk6UPIj6iDw
(password is "samara").
There's a psionics class and psionic talents, an elemental cleric class with it's own 3 spell paths (27 spells), D&D wizards with preserving/defiling rules and 8 paths based on the D&D spell schools (72 new spells), and new Dark Sun races such as Mul and Thri-Kreen etc. I also have some docs on mass combat, custom mishap tables for defilers and psions, and a bastiary with around 40-50 D&D monsters, although those last few aren;t in the docs share because I don't want my players to see them