BrowserQuest is a classic style video game written in HTML5 and Javascript by LittleWorkshop and Mozilla.
The game makes use of HTML5′s Web Workers to enable fast two-way communication between the browser and the server which is essential for a massively multiplayer game. This is achieved with HTML5 in the browser and Node.js server using the websocket-server module. HTML5′s localStorage is used to store your character’s progress. The various graphics layers (background, characters, gui) are rendered to individual HTML5 canvases from a 2D engine.
Video and links after the break