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.
ClockingIT - ClockingIT is a free hosted application, keeping track of all your tasks and the time you
Kolab Community - Kolab Groupware is a secure, scalable, reliable, flexible, full-featured collaboration suite.
Google Workspace - Google's encompassing suite of cloud-based business apps.
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
Keikai - Effortlessly Build Spreadsheet-driven Web Apps