I am looking for suggestions for an RPG system that handles character level and class level tracked separately. Ideally I would like to find something that does this based on XP spent.
For context, I'm looking to design a system that separates class level and character level. The goal is to have character level determine HP, defenses, accuracy and a few other things – "core" character stuff. Class level would determine abilities and equipment permitted. I want PC to have the capability to switch class at any time (think the Final Fantasy XI and XIV video games). XP will be used to "buy" abilities and stat increases, with only the abilities that match the current class available during play.
Right now, however, the trouble is figuring out a fair method for handling this. Clearly there is a lot of potential for bad balancing to turn the interesting strategic choices here into a boring one-best-choice situation.
As an example of how I'm imagining XP to work:
Player A has earned 600 XP. He has spent 100 XP into stats, 300 XP into Fighter stuff and 200 XP into Mage abilities. This makes his Class Level for Fighter 3, for Mage 2 and overall Character Level 6. Currently he has chosen Fighter as his active class.
I know that D&D 3 and variants of it do separate class levels at level up via multiclassing, but they don't do it based on spent XP, just choice of available classes. I know that the Warhammer RPGs do this in career tracks with ranks at XP thresholds. I am hoping that people who have further experience with games I may not have even heard of, might have recommendations for me.