Daniel Lemire and Sean McGrath note that “User personalization and profiling is key to many succesful Web sites. Consider that there is considerable free content on the Web, but comparatively few tools to help us organize or mine such content for specific purposes.” And they’ve written a paper and released prototype code on collaborative filtering.
Vogoo claims to be a “a powerful collaborative filtering engine that allows Webmasters to easily add personalization features to their Web Sites.”