Responsive Web Design has become a basic standard of web designing these days. From no where, there are now tens of Responsive frameworks which allow designers and developers to focus on core design of the application than basic boilerplate code for design.
Twitter Bootstrap has become the standard against which all Responsive frameworks are judged, and for a lot of good reasons. At the same time, there are excellent CSS frameworks like Zurb Foundation, LESS Framework etc. which offer features - be it components, code style, architecture, which can be more to one's taste and development preference.