http://dmoz.org/Computers/Programming/Languages/PHP/Scripts/Link_Management/
Booby – PHP Bookmarks/Favorites and contacts management (and other stuff). Booby is a multiuser, multilanguage, fully themeable web-based desktop application which provides online management for bookmarks/favorites, contacts, todo’s, notes and news feeds.
Directory Search – Multi-level category directory, integrated search engine, powerful control panel. [Free and commercial versions”>
PhpDig – A search engine written in PHP that uses a MySQL database backend. It features indexing of both static and dynamic pages and full text indexing.