Trillian is a proprietary multiprotocol instant messaging application.

Mailpile is a webmail client with encryption and privacy features built-in. Mailpile is free and open-source software.

Kopano is an open-source groupware application suite originally based on Zarafa.

Evolution is the official personal information manager for GNOME.

Mutt is a text-based email client for Unix-like systems.

Dovecot is an open source IMAP and POP3 email server for Linux/UNIX-like systems, written with security primarily in mind.