Flappy Bird has to be, perhaps, the best definition of an overnight success. So much so that the developers who made it ended up pulling it off the app stores as they couldn't handle the sudden coverage the game got. Luckily, for the addicted many, they put it back.

The premise of this game is, like Snake, straightforward. You just have to guide your character through an infinite series of gates, which are in different positions. To do this, you need to tap the screen. Tapping the screen causes the character to move upward. When you are not tapping, it will dive down. You gain a point for every gate you go through, and the game is over when your character collides with a gate.

Simple, yet it is excruciatingly difficult to play and do well. This was the main driver for the people who kept coming back.