jQuery UI provides abstractions for low-level interaction and animation, advanced effects and high-level, themeable widgets, built on top of the jQuery JavaScript Library, that you can use to build highly interactive web applications.
The YUI Library is a set of utilities and controls, written in JavaScript, for building richly interactive web applications using techniques such as DOM scripting, DHTML and AJAX. YUI is available under a BSD license and is free for all uses. The YUI project includes the YUI Library and two build-time tools: YUI Compressor (minification) and YUI Doc (documentation engine for JavaScript code).
Zeus a Java Swing Components Library. Provides usefull swing components for easier GUI development. Some of the components are: JConsole,JMessage,JSplash,SingleAppInstance,WindowManager,AutoResizeTableColumns,TableSorter,TypeSafe API and much more.