<sep/>inspection tool - similar to Firebug. NitobiBug runs across different browsers (IE6+, Safari, Opera, Firefox) to provide a consistent and powerful tool for developing rich Ajax applications.
If you like Firebug, but have to develop across browsers (erm, that's everybody, right?), this tool is what you have been dreaming about. Now works in IE and Safari too!
MRI is a bookmarklet for Internet Explorer 6+, and Webkit and Mozilla based browsers (including Safari, Firefox, Camino or Mozilla). Use it to test and play with selectors.
Rober O'Callahan lays out some of the conceptual issues with IE's new compatibility mechanism. He makes a good argument that this is _bad_ for IE (and the web) in the long term.