I like Into the Odd’s stripped-down ability scores: Strength, Dexterity, Charisma. 3d6 in order, of course. Hit die d8 per level. Ability scores serve as saving throws: roll under on d20 to save. Ascending AC, with 10 being unarmoured, 12 being leather, 14 chain, 16 plate. A light shield is +1, a heavy shield is +2. Attack bonus equal to level, up to +10. That’s combat out of the way.
No classes – instead, a la Knave, your abilities are determined by your equipment. You get item slots equal to Strength. You can carry armour, swords, shields, potions, spells on clay tablets, and use whatever you want.
As to spellcasting: anyone can invoke a spell by smashing the clay tablet on which it is inscribed, but one can also pay to receive the training necessary to cast without expending the tablet. A starting character could elect to have this training in lieu of a sword or something, or it could be acquired later, as a reward for doing enough tomb-robbing.
That’s enough of a framework for me to start with. More (of everything) later.