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.
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