What is Desktop Dungeons?
Desktop Dungeons is a Roguelike in the vein of Nethack re-imagined as a 2d Puzzle game. You pick your race and your class and dungeon crawl using unique spells and mechanics to try to defeat the big bad to win the game. The mechanics are finely tuned and the game difficulty as harsh and unrelenting as your favorite old school dungeon crawlers.
From their official site:
Time Waster: Desktop Dungeons,
Desktop Dungeons offers an unquestionably unique approach to roguelike games by taking compactness to the extreme. It distills the entire genre to a few core ideas which pay homage to the greats while forging new ground with gameplay similar to that of Oasis or Tower of the Sorcerer. It also features emergent complexity that rewards truly skilled and thoughtful players.