Web Starter Kit (GitHub: google / web-starter-kit, License: Apache 2.0) from Google is a boilerplate for developing responsive websites. It supports multiple devices, has a gulp.js build script, and has support for synchronising pages across devices during testing.
If you're a Node developer, then you might like the gulp.js-based environment. Typing gulp will build and optimise the current project, and gulp serve will run a server. There's also gulp pagespeed that uses Google's PageSpeed insights.
The sync feature for testing is powered by BrowserSync. BrowserSync is a Socket.IO-based Node application that automatically sends changes to pages as you edit files. It also has a gulp.js module that you can use with your own projects.
Although this is a boilerplate project, the style guide makes it look more like something like Bootstrap. If you find Bootstrap too heavy for your projects and would prefer something lighter with workflow tools, then give Web Starter Kit a try.
Using TowTruck two people can interact on the same page, seeing each other's cursors, edits, and browsing a site together. The TowTruck service is included by the web site owner, and a web site can customize and configure aspects of TowTruck's behavior on the site.
It's not currently distributed as a module on npm, so you'll need to follow the instructions in the readme to install it. There's also a bookmarklet for adding TowTruck to any page, and a Firefox add-on as well.