An add-in toolbar for InternetExplorer or MozillaBrowser that provides an automated referral service similar to (but different than) the OpenDirectoryProject.  You tell it what you like, it recommends other sites for you to visit.

http://www.stumbleupon.com/

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I wonder how they decide "on-the-fly" how to categorize pages?  How do they determine what pages you will like?

''When you install it, it gives you a browser toolbar that includes, amongst other things, two buttons called "Not-for-me" and "I like it!". The recommendations are generated from these user reviews. You can also enter descriptions of and comments on sites in their database by hitting the comment button when you visit a site. Here's what it has to say for Wiki: http://www.stumbleupon.com/url.php?url=http%3A//c2.com/cgi/wiki (BrokenLink 20120712). I think the categorizations could probably do with a little more work, but in general it's pretty good. You select topics of interest to you and they appear in a dropdown menu in the toolbar; you can select one and hit "Stumble!" and it takes you somewhere rated well by the users. So far, everything it's shown me has been really interesting. I'm impressed.''
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CategorySemanticWeb