VCF2alias is a tool to extract name and email information from VCF attachments (automatically if you use the enclosed mailcap), and writes a line (user-defined) to a file (user-defined). Originally, VCF2alias was aimed at mutt, but it should now work with any mail program that has text-file alias definitions.
eXtended Account Management System (XAMS) allows Administration of Unix, Web, FTP, DNS, and email accounts to manage a provider's typical userbase. Especially focusing on email account management, it enables you to easily create accounts, set aliases, and delegate domain administration to 2nd party resellers or customers. It uses PHP with MySQL or PostgreSQL as a backend, and is therefore able to manage tons of email accounts independently from your Unix/Linux accounts. Exim for SMTP and Courier for POP/IMAP are fully supported, but postfix, Cyrus, and qmail can be used too.
Otak provides a visual interface to command line programs that don't have one, that allows users to select arguments from a menu. For example, it can be used as an address book program with Mutt (the default), or as a phone book with SMS sending software, or even as a list of hosts for SSH or FTP.
XFMail is an X11 application for receiving electronic mail. It implements most of its email functionality internally so that it does not depend on a lot of extra packages. It supports POP3, MBOX, IMAP4, sendmail, and SMTP. It has built-in support for interfacing with PGP, GPG, ispell/aspell, faces, LDAP, and esound. It runs on most Unix variants.
Csv2vcard is a program for converting CSV (comma separated values, as exported by software such as MS Outlook) files containing contact information to the industry standard vcard format, which can be imported by most mailers and PIM software (optimized for Evolution). It's based on a Perl script by Michael MacDonald of Ximian. Csv2vcard can be used to convert any CSV format, not just the English Outlook output.
Twiggi Web Based Groupware is a Web based groupware application, written in PHP4, using MySQL as its database engine. It was originally based on the excellent TWIG project. With many on-going enhancements, it is similar to Microsoft Outlook, and features the following modules: twiggi today, Mail, Contacts, Notes, ToDo, Bookmarks, and extensive online help (available in English and German). Twiggi has full language support for German, Dutch, Italian, and English.