I noticed we had quite a few Flappy Bird clone submissions varying from direct clones to cool variations. I'm sure there are plenty more HTML5 versions of the game out there as well - these were just the ones developers submitted to Clay.io. A few have already made their round on HN.
It's interesting to see how the indie scene and game devs in general react to something like Flappy Bird.
A lot of these unfortunately don't work on mobile devices :/ I'm working to try and get more folks serious about developing for the mobile web - but it is a much more difficult task than developing for desktop-only.