GCD changes Morrowind's levelling system to make it seamless. Limits are removed from skills and attributes, and skill gain is slowed down exponentially to preserve game balance. Skills influence attributes, health and magicka directly. Characters remain diverse throughout the game, with strengths and weaknesses dependent on initial skill choices, skill increases and racial factors.
This mod works with OpenMW, but I've experienced some odd behavior at very high levels. It's been a long time so I don't remember specifics, but I vaguely recall stat increases becoming problematic once you get near or past 100.
Galsiahs Character Development.esp