Quake II Running Entirely in the Browser ↦

Quake II has been ported to HTML5/JavaScript (modern browsers only need apply; don’t even think of trying this in Internet Explorer):

In the port, we use WebGL, the Canvas API, HTML 5 <audio> elements, the local storage API, and WebSockets to demonstrate the possibilities of pure web applications in modern browsers such as Safari and Chrome.

The browser has indeed become the OS.