The Q.js toolset was developed from dissatisfaction with the existing toolsets. Not that there aren’t any good styled sliders or color pickers out there, but there is no library combining them all in one system. It is still under development but there is some very promising stuff in the roadmap.

It is built on the prototype.js. and scriptaculous libraries and features a growl-like user messaging system, color picker (based on raphaël), slider, tooltip system, draggable window and alert / confirm / prompt windowing system.

Q is using a dynamic stylesheet system. It generates the css declarations on demand and only for the modules active at that time. You can add your own declarations for any given class or object so styling is really easy.
All background images and fillers are compiled in as few as possible png images. The original vector files are provided as well so you can modify the look and feel in no time.