Born towards the end of last decade as an informal, then semi-formal collaboration between web browser vendors, HTML5 became a W3C standard in the mean time. It was still exotic in 2009 when I made [[Square_Shooter?]], but quickly became old hat. For games, its most important additions are the canvas element, and gamepad support as used in Laser Sky. Electric Rogue and Buzz Grid were also made with it, and even tools such as ASCII Mapper.
I wrote a couple of quick start guides for HTML5:
Both are now part of Game Programming Interfaces. See also these older articles:
And also these on a specific topic:
Things have changed a lot since then, but still.