Shuffledot

Shuffledot is a pocket-sized abstract strategy game somewhere between Dominoes and Go, that is simple to learn but can be played again and again. 

Players lay tiles trying to create the longest line of their colour, while confounding their opponent by breaking their line with slides.

A online version of the game is available to play for free at shuffledot.com and there are video tutorials and instructions on how to play the tabletop game there too.

The page on Boardgamegeek has forums for commenting on variants or suggesting new ones.

Included here: A single A4 pdf that's all you need to get started.