jQuery TOOLS is a set of frequently used user interface components, built with/for jQuery, to power your websites.
The library is lightweight (5.8kb) and consists of the following tools:
All the tools can be used together, extended, configured and styled which makes it very flexible.
Every feature in the library is very well documented & offers various examples to lower the learning curve.
It is also possible to download the tools you need rather than the whole package, combined in a one file.