Today JavaScript is widely used by web developers. There are a lot of libraries to add special effects, simple way to implement Ajax, complex components, forms, tabs or everything else. Here’s a collection of Ajax, Javascript and DHTML Libraries.

Prototype is a JavaScript Framework that aims to ease development of dynamic web applications. Featuring a unique, easy-to-use toolkit for class-driven development and the nicest Ajax library around, Prototype is quickly becoming the codebase of choice for web application developers everywhere.

AHAH is a very simple technique for dynamically updating web pages using JavaScript . It involves using XMLHTTPRequest  to retrieve (X)HTML  fragments which are then inserted directly into the web page, whence they can be styled using CSS. it is a subset with some very specific and useful properties, such as the lack of custom XML schemas. AHAH can trivially reuse existing HTML pages, avoiding the need for a custom web service. All data transport is done via browser-friendly HTML, easing debugging and testing. The HTML is designed to be directly embedded in the page’s DOM, eliminating the need for parsing.

dojo   is an Open Source DHTML toolkit written in JavaScript. It builds on several contributed code bases (nWidgets, Burstlib, f(m)), which is why we refer to it sometimes as a “unified” toolkit. Dojo aims to solve some long-standing historical problems with DHTML which prevented mass adoption of dynamic web application development. It allows you to easily build dynamic capabilities into web pages and any other environment that supports JavaScript sanely. You can use the components that Dojo provides to make your web sites more usable, responsive, and functional.

AjaxAC is an open-source framework written in PHP, used to develop/create/generate AJAX applications. The fundamental idea behind AJAX (Asynchronous JavaScript And XML) is to use the XMLHttpRequest object to change a web page state using background HTTP sub-requests without reloading the entire page. It is released under the terms of the Apache License v2.0.

JSAN – JavaScript Archive Network is a comprehensive resource for Open Source JavaScript libraries and software.

Ajax.NET Professional is one of the first AJAX frameworks available for Microsoft ASP.NET and is working with .NET 1.1 and 2.0. You can find here a quick guide how to get the first Ajax.NET method running.

AjaxRequest Library   is a layer over the XMLHttpRequest functionality which makes the communication between Javascript and the server easier for developers. It makes the interface more logical and consistent with what developers expect. It supports multiple simultaneous requests which will not collide with each other without any additional work from the developer.

ATLAS is  free framework for quickly creating a new generation of more efficient and interactive Web experiences that work across all the most popular browsers. With ASP.NET AJAX you can create next-generation interfaces with reusable AJAX components, enhance existing pages using powerful AJAX controls with support for all modern browsers. Continue using Visual Studio 2005 to take your ASP.NET 2.0 sites to the next level. Access remote services and data from the browser without tons of complicated script.

Bajax is a very small and simple javascript library to use Ajax on your pages. It is independent of programming language. You can put dynamic content using simple commands.

MochiKit is a highly documented and well tested, suite of JavaScript libraries. It provides the best ideas from  Python, Objective-C, etc. experience.

Code Snippets is a public source code repository. It allows to easily build up your personal collection of code snippets, categorize them with tags / keywords, and share them with the world.

DHTML API, Drag & Drop for Images and Layers A Cross-browser JavaScript DHTML Library which adds Drag Drop functionality and extended DHTML capabilities to layers and to any desired image, even those integrated into the text  flow.

DHTMLgoodies.com offers a  library of DHTML and AJAX scripts.

DHTMLX Toolkit is a JavaScript library of more than 15 Ajax-enabled components, including full-featured datagrid, tree, combobox, tabbar, menu, layout, etc. The components support the main types of functionality required for development of advanced web applications: drag-n-drop, in-line editing, clipboard operations, special techniques for handling large datasets.

Dynamic Drive is a place on the net to obtain free, original DHTML & Javascripts to enhance your web site. The site is regularly updated.

DynAPI   is an open-source project initiated by Dan Steinman, created to make cross-browser Dynamic HTML a reality. The DynAPI library uses an object-oriented approach to solve problems associated with scripting for both Netscape and Internet Explorer.

qooxdoo is a comprehensive and innovative Open Source multipurpose AJAX framework, dual-licensed under LGPL/EPL. It includes support for professional JavaScript development, a state-of-the-art GUI toolkit and high-level client-server communication.

Engine for Web Applications is an application framework for client-side development and Web applications. It provides an environment in which to develop and run JavaScript components and applications. Each Engine can be pre-built to user specifications, and components can be built into the engine itself, deployed as separate script packages, or deployed as application components.

JavaScript Libraries are created by Mark Wilton-Jones. Here you can find images, variable retention, forms, generic DHTML, movable content, menu controls, rewritable content, document and mouse effects, and games.

Javascript Toolbox is a repository of code and reusable libraries which address common needs that many web developers encounter. The code found here is based on standards but also tries to be backwards-compatible for browsers which don’t support the standards. All code on the site is written by one person, in a consistent fashion, tested thoroughly, and used in practice by thousands of web sites around the world.

Taconite is a framework that simplifies the creation of Ajax enabled Web applications. It’s a very lightweight framework that automates the tedious tasks related to Ajax development, such as the creation and management of the XMLHttpRequest object and the creation of dynamic content. Taconite can be used with all modern Web browsers (Firefox, Safari, IE, Opera, and Konqueror, to name a few) and can be used with any server-side technology including Java EE, .Net, PHP, or any language that lets you return XHTML.

JonDesign’s Smooth SlideShow Library is a javascript slideshow system that allows you to have a simple and smooth (cross-fading…) image slideshows and/or showcases on you website.

jQuery – New Wave Javascript is a fast, concise, JavaScript Library that simplifies how you traverse HTML documents, handle events, perform animations, and add Ajax interactions to your web pages.

JSL: JavaScript Standard Library is a single and small file ( IE4 compatible packed version: 7.77 Kb ) with some JavaScript 1.6 standard methods or functions that are not present on some browsers. You could just add JSL even before your scripts to add portability or more compatibility, then you don’t need to rewrite anything. JSL is compatible with every browser that supports at least JavaScript 1.2.

Kabuki (a.k.a Zimbra) AJAX Toolkit is a client developer library, similar in style to traditional object-oriented widget libraries like Eclipse’s SWT, albeit for JavaScript.

DHTML Kitchen is a resource for ready-made or custom-built DHTML scripts.

The X Library is a collection of loosely-bound, cross-browser, Javascript functions and objects. It is intended to be a resource from which you pick and choose – you do not have to include the entire library in your application. It contains core DOM/Style functions, unobtrusive enhancements, utility functions, objects such as menus and tab panels, and also has some experimental stuff. I’ve been developing this library since 2001 (I started its predecessor around 1999). Thanks to thousands of people like yourself X has been extensively tested on a wide range of operating systems and browsers. Thanks to your contributions X continues to improve, grow and evolve.

liberty is a JavaScript Basic library to make web development with JavaScript comfortable.

moo.fx is a superlightweight, ultratiny, megasmall javascript effects library, to be used with prototype.js or the mootools framework. It’s very easy to use, cross-browser, standards compliant, provides controls to modify any CSS property of any HTML element, including colors, with builtin checks that won’t let a user break the effect with multiple, crazy clicks. Optimized to make you write the lesser code possible, the new moo.fx is so modular you can create any kind of effect with it.

overLIB is a JavaScript library created to enhance websites with small popup information boxes (like tooltips) to help visitors around your website. It can be used to provide the user with information about what will happen when they click on a link as well as navigational help (see the examples below).

TurboWidgets are JavaScript client-side controls that provide a rich user-interface experience for AJAX-style web applications. Built on top of the popular Dojo Toolkit, TurboWidgets are designed for ease-of-use and flexibility.

overlibmws DHTML Popup Library Download and Test Directory for the overlibmws DHTML Popup Library

PlotKit – Javascript Chart Plotting is a Chart and Graph Plotting Library for Javascript. It has support for HTML Canvas and also SVG via Adobe SVG Viewer and native browser support. PlotKit is fully documented and there is a quick tutorial to get you started. PlotKit is a complete rewrite of CanvasGraph. It is better structured and supported.

qForms JavaScript API is one of the most complete JavaScript API for interfacing forms. The qForms API has been designed to make forms easy to work with. It simplifies tasks HTML developers normally find tricky to handle.

Zapatec AJAX Suite includes mature, feature-rich widgets to cover all your development needs. Modular architecture gives you the flexibility to use a few widgets today and migrate to using the full suite on an as-needed basis. No need to learn a proprietary XML dialect or a complicated new platform — use the same tools you currently do, like HTML, CSS, JSON and more.

Rico provides responsive animation for smooth effects and transitions that that can communicate change in richer ways than traditional web applications have explored before.

Ruby on Rails is a full-stack framework for developing database-backed web applications according to the Model-View-Control pattern.

Sajax is an open source tool to make programming websites using the Ajax framework — also known as XMLHTTPRequest or remote scripting — as easy as possible. Sajax makes it easy to call PHP, Perl or Python functions from your webpages via JavaScript without performing a browser refresh. The toolkit does 99% of the work for you.

sardalya is a cross-browser compatible system which is designed to work in all DOM-supporting browsers. s@rdalya has been tested with Internet explorer 6, Netscape navigator 6-7-8beta, Mozilla 1.5-FireFox 1.0.3, Opera 7.0-7.2-8Beta and more.

The Solvent is a cross-browser AJAX application toolkit written in JavaScript. The Solvent is provided as modules or as an entire toolkit. The projects focus is to promote robust web applications and enable rapid web development.

script.aculo.us provides you with easy-to-use, cross-browser user interface JavaScript libraries to make your web sites and web applications fly.

Spry Framework for Ajax is a JavaScript library that provides easy-to-use yet powerful Ajax functionality that allows designers to build pages that provide a richer experience for their users. It is designed to take the complexity out of Ajax and allow designers to easily create Web 2.0 pages.

Tabtastic is a simple way to implement tabs on your page using CSS, a little JS, and semantic markup which degrades gracefully on browsers with CSS unavailable or disabled. Not only is it easy to use and accessible for screen-readers, but it supports multiple (nested, even) tabsets on the same page and allows users to bookmark the page loading to a specific tab.

Tacos library project provides components and ajax behaviour for the Tapestry java web application framework. Most of the functionality is based on the exceptional dojo javascript library.

ThyApi is an api to allow the developement of better user interfaces for web applicaticions, Using javascript and Ajax, it allows a complete visual interface definition using CSS and encapsulates all objects data manipulateion. Build over DynApi.

TwinHelix offers DHTML and JavaScript, XHTML, CSS and CGI projects.

Yahoo! User Interface 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. The YUI Library also includes several core CSS resources. All components in the YUI Library have been released as open source under a BSD license and are free for all uses.

Zebda is a general purpose javascript library built on Prototype 1.4.0.

Zephyr is an ajax based framework for php5 developers.

ZK is an open-source Ajax Web framework that enables rich user interface for Web applications with no JavaScript and little programming.