Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.
Taskbook - Like Trello but for the Terminal
Roundcube - Web-based IMAP email client
dstask - Command line todo list with git sync
Microsoft Exchange Server - Microsoft Exchange Server is a messaging and collaborative software product developed by Microsoft.
Calcurse - Calcurse is a calendar and scheduling application for the command line.