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.
FinancialForce HCM - FinancialForce.com provides cloud back-office applications for Salesforce CRM.
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
Vibe HCM - Vibe HCM is a recruiting and employee engagement platform.
mailcow - An open source mailserver suite.
BMC Remedy - IT Service Management Suite