Kontact - KOrganizer - KOrganizer is the calendar and scheduling component of Kontact, the integrated personal information...
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
CalenGoo - Features | 1.0.175 for Android™
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.
Rainlendar - Rainlendar - Customizable desktop calendar
Microsoft Exchange Server - Microsoft Exchange Server is a messaging and collaborative software product developed by Microsoft.