I spent yesterday afternoon creating a Chrome extension using Adnan Topal’s extractCSS library. I found extractCSS.com a few months back, I think via Hacker News, and thought it was a cool idea. It lets you paste a chunk of HTML code and it will extract the CSS classes, IDs, and inline styles used in that HTML. It produces a skeleton stylesheet with rules for those IDs and classes, and inline styles already filled in.
It seems like just the thing to use if you want to build a child theme for a WordPress site, for example, or do other derivative work on an existing site’s framework. The annoying thing about extractCSS.com though is that you have to paste HTML code, you can’t just point it at a URL and let it get the HTML for you. My Chrome extension lets you get a skeleton stylesheet for any page you’re viewing, just by hitting a button. No viewing source code or copy/pasting anything.