Xmarks (formerly Foxmarks) is a free password- and bookmark-syncing tool. Users who want to share the same set of bookmarks and site passwords can install this browser plug-in and it will keep information the same across multiple machines. Users can also retrieve all their information from the cloud if their machines suffer a major data disaster.
In 2009 Xmarks hopped into site discovery by taking all of the bookmarking information from its users and turning it into a public database of sites. It created a site discovery tool that shows you what sites are like the one you're on by seeing what other users have bookmarked.