stumbleupon.com is a form of a search engine known as a discovery engine. It was founded by Garrett Camp, Geoff Smith, Justin LaFrance and Eric Boyd in November 2001. Users can search and discover web pages, photographs and videos. In 2011 it has crossed twenty billion registered users. Registeration is free on the site. It has a nice eye catchy logo and a simple layout. Its user friendly interface makes it easy to handle especially for new users.
It was purchased by eBay in the year 2007 but was purchased by its founders again in 2009. It even provides services like advertising on its site apart from Stumble Thru and Stumble Upon videos. Stumble thru is a service which allows users to view content on youtube, Wikipedia, the onion and The Public Broadcasting Service. In 2009 it launched su.pr which is a URL shortening service.
The site also provides the user a chance to rate the websites and even leave a review.