1. Yahoo! YUI Library
YUI, currently in its third edition, is a constantly updated (by its large team of developers) UI library that’s choc-full of features, tools, and packs a multitude of components, utilities, modules and controls.
3. iUI: iPhone User Interface Framework
4. Alloy UI
Feature rich UI frameworks, built on YUI 3 and to some degree on YUI 2, which comprises a wide array of components – more than 60 in all – that range from utilities to sugar layers to full-blown UI widgets. Its controls include: Image Gallery, Dialog, Treeview, Panel, AutoComplete, Button, Calendar, Toolbar… and much more.
A popular UI kit that extends the Prototype Framework by adding visual effects, user interface controls, and utilities via the DOM.
It has been built on Prototype 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 systems.
7. Dijit – The Dojo Toolkit
8. JxLib based MotoTools
9. Sigma Ajax UI Builder
10. MochaUI – A Web Application User Interface Library