Kopano
Open Source
Kopano is an open-source groupware application suite originally based on Zarafa.
MDaemon Messaging Server
Commercial
MDaemon Messaging Server is an e-mail server software for Windows.
hMail Server
Open Source
hMailServer is a free open source email server for Microsoft Windows.
Zarafa
Commercial
Zarafa is an open-source groupware application.
Compare Microsoft Exchange Server with alternatives
Compare Kopano and Microsoft Exchange Server and decide which is most suitable for you.
Compare hMail Server and Microsoft Exchange Server and decide which is most suitable for you.
Compare MDaemon Messaging Server and Microsoft Exchange Server and decide which is most suitable for you.
Compare Zarafa and Microsoft Exchange Server and decide which is most suitable for you.