My favorite three responsive web design frameworks are Bootstrap, Foundation and Gumby, in that order. But sadly, development of Gumby has recently ceased. And these frameworks aren't necessarily the right solution for every project. For example, if you want to rapidly create a responsive design in the shortest possible time, you should consider a lightweight framework. Here are four of the most promising complete, lightweight, intuitive, and responsive CSS frameworks. They are all released under the MIT License, a free software license originating at the Massachusetts Institute of Technology.