Desktop Dungeons

Here is an excerpt from Desktop Dungeons' Steam description:

Desktop Dungeons is a quick-play, roguelike-like puzzle game that gives you 10-20 minutes of dungeon-crawling action per serving. Casual players can enjoy endless coffee-break gaming sessions in infinitely random dungeons, while hardcore enthusiasts can unearth the game’s subtleties and tackle challenges of unrealistic viciousness. Down all paths lies frequent death, easy accessibility and the urge to play just one more dungeon.

Now with new content and quests, new classes (that's 21 total now if you've been keeping count) and a new way to play: For the first time ever, compete against your friends (or the world at large) in the seeded Daily Dungeon.