I'm fairly sure this game exists, but I can't figure out for the life of me which one it is. I know it's not Darker Dungeons, Labyrinth Lord, or LotFP, because I just checked them before posting this.
It's a retro-clone of old D&D, Rules Cyclopedia type stuff (though perhaps without the whole depth of the RC). It has ascending AC, attack bonuses, and saves. It uses Fort, Reflex, and Will instead of the old Paralyze/Petrify set. Can't remember how it handled thief skills. Hit points and spells were much more OD&D than 3E.
I would swear that I saw this game and just can't come up with the name, but I'm open to the possibility that I just imagined it.