Paper Apps: Dungeon
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How it works: A paper-and-pencil dungeon crawler printed in a 3x5" inch memo pad. Create your character, roll the pencil dice, conquer the dungeon. Had a very sucessful Kickstarter run.
Why it's clever: Each level is programmatically generated with Python and Drawbot, so each one is unique. If you play multiple books, each one will be different. Also, instead of a dice, they offer a D6 pencil, which is pretty dang clever.
Price: $7.99 (plus a few bucks more for the pencil)