Mozilla is sponsoring a contest to build the best game using the Goo toolset. The Goo tools looks like a good HTML5 toolset for designers and programmers. Give it a try!
https://blog.mozilla.org/blog/2013/12/05/unleash-the-game-creator-in-you-by-entering-our-holiday-gaming-competition/
It is worth noting that rumors are swirling around the likelihood that Unity will also be developing an HTML5 pipeline. What is clear is that HTML5 casual gaming will be huge for indie developers in the mobile market.