Flappy bird concept is a bit old but it's still enjoyable and could be a great success if linked to bitcoins.
Someone already tried that, though it seems not to have been such a great success so far, unfortunately: (
https://bitcointalk.org/index.php?topic=668391.0). Gravitate apparently decided to take a step back and start offering fiat currency to get more players first, and leave bitcoin rewards for later.