Hackmaster 5E. I know for many it's so crunchy they wont even attempt to play it, but it does so many things right it's hard not gush about it every chance I get.
Just look at how the attributes are used:
Strength: Damage, Encumbrance, Feats of Strength, Weapons that can be held
Intelligence: Attack Modifier, Building Points (used to buy skills, feats, or raise attributes)
Wisdom: Initiative, Defense, Mental Saving Throws, Building Points
Dexterity: Initiative, Attack Modifier, Defense Modifier, Dodge Saving Throws, Feats of Agility
Constitution: Physical Saving Throws, Hit Points, Threshold of Pain (withstand large blows knocking you out)
Looks: Charisma, Starting Honor and Fame
Charisma: Turning (Cleric), Morale, Building Points, Starting Honor, Maximum Proteges
Some other brilliant touches:
No combat rounds, everyone takes turns depending on fast their attack speed
Fighters have to level up to become a Paladin
Armor makes you easier to hit, but absorbs damage
Shields are really good at blocking hits, but powerful blows can break them and carry over to you.
The longer you go without a rest, the higher your EXP bonus will be
Attributes have a chance to improve every level
Gold always in demand thanks to being needed for better gear/repairs and leveling up
Intricate Wound system, making combat dangerous and gritty, no matter HP values
Exploding Dice! (if you roll the highest value, roll again at - 1 and add it to the total)
I could go on and on. If you enjoy clever takes on D&D rules, I think this is worth it just to read through for houserule inspiration.