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Looking at Ultima Online a little more it has a skill-based system instead of XP/levels which is something I've thought about quite a bit. I've always felt like it makes more sense to level up the skills that actually get used... but again games went another direction because of the whole "just because it's realistic doesn't mean it's a good idea for gaming" situation.

I remember Ultima but I never actually played it.
Missed opportunity!
It was definitely the monthly fee that threw me off and convinced me it couldn't be worth it.

I was thinking of the single player games but yeah ultima online might be closer to your vision