"Twitter Bootstrap is a free collection of tools for creating websites and web applications. It contains HTML and CSS-based design templates for typography, forms, buttons, navigation and other interface components, as well as optional JavaScript extensions.
It is the most popular project on GitHub and has been used by NASA and MSNBC among others." (Wikipedia)
Normally, when you read "getting started" instructions for Twitter Bootstrap, you're told to download various things from various sites. Then you're told to set up various folders and files, etc. What if it could be much simpler than that? Spend 7 minutes with me in this (silent) screencast and you'll see a complete development environment for developing applications with Twitter Bootstrap:
Two things that could be added to the movie are the JavaScript debugger, the support for responsive design via switching between form factors in the embedded browser and Chrome with the NetBeans plugin, as well as how to convert the application to a native Android or iOS package via in-built Cordova support.