BoltJS is a UI framework that’s being built by Facebook for the purpose “helping developers build fantastic mobile web applications in HTML5 and Javascript,†as you can read for yourself here. It is written entirely in JavaScript and runs in the browser, meaning no backend processing is required. And guess where the focus of the project lies right now: mobile WebKit browsers — just like Project Spartan.
Besides the mentioned Weather App (which has been removed from BoltJS), Google Cache shows one more example: A sample Maze game.