So cool ! When I found this lib for Ajax by chance, I can not stop to copy it here.

Yahoo! User Interface Library components fall into three groups: Utilities, UI Controls, and CSS resources.

YUI Utilities

The YUI Utilities simplify in-browser devolvement that relies on cross-browser DOM scripting, as do all web applications with DHTML and AJAX characteristics.

  • Animation: Create "cinematic effects" on your pages by animating the position, size, opacity or other characteristics of page elements. These effects can be used to reinforce the user's understanding of changes happening on the page.
  • Connection Manager: This utility library helps manage XMLHttpRequest (commonly referred to as AJAX) transactions in a cross-browser fashion, including integrated support for form posts, error handling and callbacks. Connection Manager also supports file uploading.
  • Dom Collection:The DOM Utility is an umbrella object comprising a variety of convenience methods for common DOM-scripting tasks, including element positioning and CSS style management.
  • Drag & Drop: Create draggable objects that can be picked up and dropped elsewhere on the page. You write code for the "interesting moments" that are triggered at each stage of the interaction (such as when a dragged object crosses over a target); the utility handles all the housekeeping and keeps things working smoothly in all supported browsers.
  • Event: This sophisticated manager class gives you easy and safe access to browser events (such as clicks and key presses). The Event package also includes the Custom Event object, a mechanism for publishing and subscribing to interesting moments in your own application flow.
YUI Controls

The YUI Library Controls provide highly interactive visual design elements for your web pages. These elements are created and managed entirely on the client side and never require a page refresh.

YUI Controls include:

  • AutoComplete: The AutoComplete Control allows you to streamline user interactions involving text-entry; the control provides suggestion lists and type-ahead functionality based on a variety of data-source formats and supports server-side data-sources via XMLHttpRequest.
  • Calendar: The Calendar Control is a graphical, dynamic control used for date selection.
  • Container: The Container family of controls supports a variety of DHTML windowing patterns including Tooltip, Panel, Dialog and SimpleDialog. The Module and Overlay controls provide a platform for implementing additional, customized DHTML windowing patterns.
  • Logger: The YUI Logger provides a quick and easy way to write log messages to an on-screen console, the FireBug extension for Firefox, or the Safari JavaScript console. Debug builds of YUI Library components are integrated with Logger to output messages for debugging implementations.
  • Menu: Application-style fly-out menus require just a few lines of code with the Menu Control. Menus can be generated entirely in JavaScript or can be layered on top of semantic unordered lists.
  • Slider: This control provides a generic slider element that enables the user to choose within a finite range of values on one or two axes.
  • TabView: TabView allows you to transform clean, semantic markup into a rich tabbed-navigation control.
  • TreeView: The TreeView control produces a content tree whose nodes can be expanded and contracted by user interaction (and by script, where necessary). The nodes can contain links or custom properties and can be loaded dynamically. The display of the node elements can be customized with CSS to create a folder view, to-do task list, or other visual treatment.
YUI CSS Resources

We've thought a lot about how to standardize our CSS approach to work across A-Grade browsers. As part of the YUI Library, we're sharing with you the basic building blocks we promote here at Yahoo! for creating clean, flexible layouts that play well across browsers.

  • CSS Grids: With three preset page widths (and the ability to set custom widths easily), with seven core templates, and with the ability to nest subdivided regions of one to four columns together, CSS Grids offers almost 200 preset layouts and an unlimited number of custom permutations that work across all A-grade browsers. Minimized file weight: about 3KB.
  • CSS Fonts: The Fonts package provides standardized cross-browser font families and size rendering.
  • CSS Reset: Use these CSS declarations at the top of your CSS to remove margins and standardize cross-browser rendering on common elements, neutralizing browsers' built-in stylesheets (and the subtle cross-browser differences they introduce).

http://www.yui-ext.com/forum/
http://developer.yahoo.com/yui/