- Zentyal (community & commercial editions)
- Top 5 Open Source Alternatives to MS Exchange:
- Citadel Groupware Server (MS Outlook connector for Citadel)
- Open-Xchange
- VMware Zimbra (+outlook sync)
- SOGo Groupware suite
- Zarafa
- + OpenChange
- IMAP Groupware Servers:
- Bynari Server (BCS)
- Citadel
- Kolab
- AtMail
- FastMail
- Kerio
- Univention Corporate Server (UCS)
- Zarafa
- Cyrus IMAPIceWarp Unified Communications Server
- MS Exchange Server Alternatives and Similar Applications