It's the top free App on both iPhone and Android devices. And if you have played Flappy Bird, you've likely experienced the fun and frustration that is making the game so popular.
The concept is simple: flap your wings to fly. Players tap to flap and help the bird avoid obstacles. The goal is to get four medals: Bronze, Silver, Gold (hard), Platinum (very hard).
Its developer, Dong Nguyen, says the game was first released in May 2013; it's been downloaded 50 million times.