Protovis - Visualization toolkit for JavaScript using SVG
http://vis.stanford.edu/protovis/ex/
MSFast - Browser performance tool for IE
http://code.google.com/p/msfast/
JavaScript InfoVis Toolkit
http://thejit.org/demos/
jQuery Tools
http://flowplayer.org/tools/demos/index.html
jQuery Expose - HTML element lightbox
http://www.flowplayer.org/tools/expose.html
JavaScript RegExp based highlighting for MooTools and jQuery
http://devthought.com/blog/client-side/2009/04/javascript-regexp-based-highlight...
Jx Lib - Mootools Javascript UI
http://jxlib.org/
Speed/validity selectors test for Javascript frameworks
http://mootools.net/slickspeed/
Poster - Firefox add-on tool for sending POST requests
https://addons.mozilla.org/en-US/firefox/addon/2691
Mootools Mocha UI - Javascript Framework
http://mochaui.com/