Dungeon Delvers is a one-page D&D variant.

It's just about that simple.

It has rules for attacks and saves, 4 classes, 3 races, spells, healing, conditions, and monsters. The system uses only a d6. There's even a rock-paper-scissors system for rolling a d6!

The basic system: roll 1d6 each for the 6 classic abilities. Attack rolls succeed on 5-6. Saves try to roll less than or equal to the relevant ability.