Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.

Cryoserver - Cryoserver is an all-in-one email archiving solution that empowers you to preserve your email in a tamper-evident archive, making you transform your data into a useful archive for everyday use.

Roundcube - Web-based IMAP email client

Gmvault - Backup the emails in your Gmail account.

Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.

imapsync - Console-based utility for migrating IMAP mailboxes.