StumbleUpon is a discovery engine (a form of web search engine) that finds and recommends web content to its users. Its features allow users to discover and rate Web pages, photos, and videos that are personalized to their tastes and interests using peer-sourcing and social-networking principles. Toolbar versions exist for Firefox, Google Chrome, Opera and Internet Explorer, but StumbleUpon also works with some independent Mozilla-based browsers. It also works with Safari. Native mobile StumbleUpon apps exist for iOS, Android, and the Amazon Appstore.
StumbleUpon uses collaborative filtering (an automated process combining human opinions with machine learning of personal preference) to create virtual communities of like-minded Web surfers. Rating Web sites update a personal profile (a blog-style record of rated sites) and generate peer networks of Web surfers linked by common interest. These social networks coordinate the distribution of Web content, so that users “stumble upon” pages explicitly recommended by friends and peers. Giving a site a thumbs up results in the site being placed under the user’s “favorites”.
Users rate a site by giving it a thumbs up, thumbs down selection on the StumbleUpon toolbar, and can optionally leave additional commentary on the site’s review page, which also appears on the user’s blog. This social content discovery approach automates the “word-of-mouth” referral of peer-approved Web sites and simplifies Web navigation.
Miłosz Szarek @ StumbleUpon