Mailafar is a mail server designed for use in difficult communication environments providing a full set of Internet email protocols, web mail, web admin, dial-in and wireless LAN access control. It will run on Linux, FreeBSD and Windows.
libmail is a C library intended to help programmers when adding mail checking and retrieving capabilities to their applications, supporting popular mail protocols like IMAP and POP3 as well as *nix-like mailboxes.
LIMeTool (pronounced like the fruit), is intended to be a simple and easy interface for managing accounts on an integrated Sendmail/LDAP/Cyrus IMAP installation. It's written in PHP and is realitively easy to configure and expand.