BookmarkSync is the only FREE and OPEN-SOURCED real-time automatic synchronization service that allows you to access your bookmarks or favorites from any computer or any browser, without changing the way you use the Internet.
This site is running the BookmarkSync server; users will need to download the free BookmarkSync client for their platform. Users interested in running their own private servers (PHP w/MySQL) should visit the SourceForge project page for further information.