There's been a recent surge in HTML5 development thanks in large part to Apple not supporting Flash for its iPad.
A group working at Google decided to devote their 20 percent time to making a version of Quake II that's playable through an HTML5-compatible browser without the need for a plugin.
Google's Chris Ramsdale wrote in a blog post:
While we've seen more impressive efforts from a browser through id Software's Quake Live, it requires a special custom plugin. This work from Google showing off HTML5 bypasses the need for custom software and plays it through right into Safari or Chrome. Sadly, Firefox doesn't support the necessary HTML5 required for this tech demo.