From OpenDarwin (thanks to Dave for the link):
I would like to introduce a new addition to the WebKit open source tools—a JavaScript debugger. Drosera, named after the largest genera of bug eating plants, lets you attach and debug JavaScript for any WebKit application—not just Safari.
One of the unique things about Drosera, like the Web Inspector, is that over 90% of it is written in HTML and JavaScript. This is a true testament of what you can do with web technologies today and the rapid development that WebKit allows.