cssQuery() is a powerful cross-browser JavaScript function that enables querying of a DOM document using CSS selectors. All CSS1 and CSS2 selectors are allowed plus quite a few CSS3 selectors.
scriptaculous - http://script.aculo.us/
script.aculo.us provides you with easy-to-use, cross-browser user interface JavaScript libraries to make your web sites and web applications fly.
What's inside? animation framework, drag and drop, Ajax controls
DOM utilities, and unit testing. It's an add-on to the fantastic Prototype framework.
xpath - http://code.google.com/p/ajaxslt/
xpath is part of ajaxslt: Pure javascript implementation of XSLT and XPath
AJAXSLT is an implementation of XSLT in JavaScript. Because XSLT uses XPath, it is also an implementation of XPath that can be used independently of XSLT. This implementation has the advantange that it makes XSLT uniformly available on more browsers than natively provide it, and that it can be extended to yet more browsers if necessary.
AJAXSLT is interesting for developers who strive aggressively for cross browser compatibility of their advanced web applications.
This implementation of XSLT operates at the DOM level on its input documents. It internally uses a DOM implementation to create the output document, but usually returns the output document as text stream. The DOM to construct the output document can be supplied by the application, or else an internal minimal DOM implementation is used. This DOM comes with a minimal XML parser that can be used to generate a suitable DOM representation of the input documents if they are present as text.
jsunit - http://www.jsunit.net/
JsUnit is a Unit Testing framework for client-side (in-browser) JavaScript. It is essentially a port of JUnit to JavaScript. Also included is a platform for automating the execution of tests on multiple browsers and multiple machines running different OSs.
strands - http://www.xucia.com/strands-doc/overview.html
Strands adds coroutine and cooperative threading support to the JavaScript language that enables blocking capabilities for asynchronous event callbacks. This makes asynchronous code refreshingly readable and comprehensible.
Dojo toolkit - http://dojotoolkit.org/
The Dojo Toolkit is an open source modular JavaScript library (or more specifically JavaScript toolkit) designed to ease the rapid development of cross platform, JavaScript/Ajax based applications and web sites.
Prototype: http://www.prototypejs.org/
http://prototype.conio.net/ ??
Prototype is a JavaScript Framework that aims to ease development of dynamic web applications.