TraceKit : Not all browsers support stack traces on error objects, but TraceKit squeezes out as much useful information as possible and normalizes it.
chromeless : The chromeless project is an experiment into making it possible to build a web browser using only web technologies, like HTML, JavaScript, and CSS.
SlimerJS : A scriptable browser for Web developers
A JavaScript file you can insert into your pages to simulate the Firebug console in browsers that are not named Firefox.
