Thinking about renaming the six classic D&D abilities to something with a more direct meaning. Not really free-form like Fate or Over the Edge (a system I really like) more specific to your class.
It started out as this:
STRENGTH = FIGHT
DEXTERITY = SNEAK
CONSTITUTION = SURVIVE
WISDOM = BLESS
INTELLIGENCE = CAST
CHARISMA = CHARM
But then I thought about taking it a bit further. Why does a Thief need CAST if you're not using magic? Or a magic-user having bless?
How about a 'You Pick Six' or UPS system;-) where you choose the six most important abilities for your class.
So, for example, a Fighter will have some different abilities than say a Cleric.
There would be the typical pre-packaged classes. But you could customize easily as well.
I would have a seventh stat called luck, which covers rolls outside of those defined by your six ability scores.
Let's say you have a magic-user with no fighting ability. Roll equal/under Luck stat. But you're really only going to want to use this as a last option, because there is a severe chance of critical failure. But at the same time, there's always a chance for success.
Basically, to take an action roll equal or under your ability. It's like Pendragon where you want to roll as high as you can, without rolling over. But there is a difference in that there is a lower threshold as well (like Unknown Armies, but using a d20). Also you automatically miss/fail with a 1.
Back to the magic-user with a Luck score of 11. You unfortunately are in a combat situation and are forced to use a knife to fight off an enemy. This is where Luck comes in. To hit the enemy you need to roll an 11 or under. But you also have a +4 modifier which goes at the bottom. So you would need to roll 6-11 to succeed (1 is always a failure +4 for the modifier).
For spells the Magic-User uses Cast. Let's say you have a 15. Roll 'between' for the spell to be cast. 15 is a critical success (you could have 1 always as a critical failure). Also the level of spell counts as a modifier. You are casting a 1st level spell, the roll needs to be 3-15 to succeed. A 2nd level spell is 4-15 and so on. If you roll above the number nothing bad happens, you simply didn't cast it. However a roll below causes some sort of misfire (that's where some fun tables or ad lib comes in).
There are three saves (similar to that in 3e D&D) which covers reactions. Not sure if these should be specific to classes as well. Again you could use luck to cover anything outside of these using the same principle.