Pairs

Pairs is a little card game which uses a simple deck of numbered cards. It has inspired several other games using the deck. There are now several fun decks available with various whimsical card designs. 

Since the cards are super-simple — just numbers, without even suits — I created a print-and-play deck of tiny cards for my own use, so that I could fit cards with rules summaries for various games using the deck into a regular deck box.