BrowserSpy

"BrowserSpy can tell you all kinds of detailed information about you and your browser. Stuff like the version of your browser. What kind of things it supports and what it doesn't support. Furthermore it can provide you detailed information about JavaScript, Java, Plug-ins, Components, Bandwidth, Language, Screen, Hardware, IP, Cookies, Web Server, and much more...."

Well, maybe not so much info about you, as your browser, and what websites learn about it when you visit. Good to know about all the info those browser features like Java, Javascript, and ActiveX, reveal about your system.