A few months ago, I published Dungeon Delvers, a retroclone that simplifies classic D&D down to just ability scores and a single d6 roll.
The system is so straightforward, in fact, that I’ve put it onto a deck of cards. There’s a card for each class, each condition (stunned, immobilized, constitution drain, etc.), and spell. There are even cards to track how many hits you’ve taken, cards to replicate a d6 roll, and the rules are on cards, too.
I’ve released the deck as a complete deck of cards (USD $15) and as a print-and-play PDF (pay what you want).
To celebrate, I’m running a contest. For every 10 sales I make of the physical cards (or of the PDF at $5 or more) by midnight this Friday, 17 January 2014, I’ll make 5 monster cards, and add them to the deck.