Openwebmail is a simple Webmail system which uses the POP3 protocol.
Horde is a powerful Webmail system which uses IMAP. It offers an outlook-like interface, and can be used in conjunction with other mail boxes (for example it can be used where you want to sync email between your mobile, webmail and your local computers mail box.
Network Savvy’s customer management system. You can check your account history, modify your email addresses etc.