As part of the redesign of CATS for the Milo project, we chose the CSS framework Bootstrap from Twitter. There are numerous CSS frameworks out there, but Bootstrap distinguishes itself by being designed for web applications.
You can think of it as the building blocks of an application. The framework provides the visual representation (and structural HTML/CSS) for common application elements like tabs, menus and modals that aren’t provided natively by the browser. You don’t have to redesign all these from scratch. It’s kind of like designing for a native OS, where the interface elements are predefined. Additionally, Bootstrap takes the headaches out of cross-browser compatibility.
Bootstrap got us moving quickly. We had originally scheduled a lengthy design process, but Bootstrap let us skip that and jump right into prototyping. In a matter of about two weeks we were able to move to real code.
Bootstrap is an excellent starting point but can also be customized to meet the specific needs of an application. Check it out.