Kolab Community
Open Source
Kolab is a free and open source groupware suite.
Zimbra Collaboration Suite
Freemium
Zimbra offers an open source email platform for the enterprise.
SOGo
Open Source
SOGo (Scalable OpenGroupware.org) is an open source collaborative software (groupware) server with a focus on simplicity and scalability.
Microsoft Exchange Server
Commercial
Microsoft Exchange Server is a mail server and calendaring server.
Compare OX Open-Xchange with alternatives
Compare Kolab Community and OX Open-Xchange and decide which is most suitable for you.
Compare SOGo and OX Open-Xchange and decide which is most suitable for you.
Compare Zimbra Collaboration Suite and OX Open-Xchange and decide which is most suitable for you.
Compare Microsoft Exchange Server and OX Open-Xchange and decide which is most suitable for you.