Searching for a Global Address Book?

dweezle37 asks: "For the past few years I have been searching for an all inclusive Global Address Book. The main features I've looked for are: Global Access (most likely Web), possible integration into external programs for email address lookup and mail merge (i.e. Mail Clients, Office Suites, etc.), fully customizable (add/remove fields), and based on a standard protocol (i.e. LDAP, SQL, etc.). An open source project would cater best to being "fully customizable". What have others found or been using? Does this project exist?"