Sigma Ajax UI Builder
JxLib based MooTools
Dijit - The Dojo Toolkit
Dijit based on Dojo, Dojo also learn a good starting point for expansion. Can be used to create a very nice Web 2.0 GUI. Support multiple languages, and even support the direction of various languages and writing on the localization of numbers, dates and so on.
jQuery Tools is a very lightweight (2.5kb) of the common UI library, support the following jQuery object, Tabs, tool tips, scroll bars, layers, nested forms, and Flash.
jQuery UI on jQuery, contains three categories, accessories, some built-in UI objects; effect, imposed on the various web pages animation objects (such as blast effects); mouse interaction, such as drag and drop.
Prototype UI Prototype-based and Script.aculo.us, including multiple modules (carousel, Modal window, shadow, right-click menu, etc.), each module can be installed separately.
Qutensil still under development, but the road map has shown some remarkable things, based on Prototype and Scriptaculous, including news, palette, slider, tool tips, and warnings can drag and drop window, confirm, prompt, etc. window.
script.aculo.us is a popular set of UI tools, based on the Prototype framework, provides visual effects such as, UI controls, and DOM-oriented tools.
AlloyUI is a feature-rich UI framework, based on YUI 3, based in part on YUI 2, contains a rich set of (over 60) UI components, such as image libraries, dialog box, tree structure, panel, auto-complete, button, calendar controls, toolbars, etc..
iUI: iPhone UI Framework
XUI is a mobile Web applications for lightweight, minimalist, highly modular framework. The reason it is very lightweight because it only support the mobile browser, cross-browser support for all of the code have been stripped. It is designed for front-line mobile Web browser, such as Webkit, Fennec and Opera, and intends in the future of the mobile IE, and Blackberry support.
Yahoo! YUI Library
Yahoo! YUI Library can be described as the father of all the Web UI, reliable, feature-rich, has now developed to version 3. It has a huge development team, introduced a wealth of features, in terms of functionality, unmatched.