The game is simple. Just about anyone can play it. The appearance is no frills, two-dimensional with basic graphics. The file size is small, just 2.83 MB. But it is just that simplicity and ease of use that has made Onet, a game for mobile devices, appeal to so many people. Four million users have downloaded the free application from the Google Play Store.

Onet is a puzzle game in which players match pictures. To beat the level, you match all th