The best Calendar alternative to OpenChange is Nextcloud Hub, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to OpenChange and six of them are Calendar Apps so hopefully you can find a suitable replacement. Other interesting Calendar App alternatives to OpenChange are Zimbra Collaboration Suite, grommunio, SmarterMail Mail Server and OBM.
Nextcloud is the most deployed on-premises file share and collaboration platform. Access & collaborate across your devices. As fully on-premises solution, Nextcloud Hub provides the benefits of online collaboration without the compliance and security risks.
Zimbra Collaboration is an open, secure collaboration tool for email, calendaring, tasks and more. With the most innovative web application available today, Zimbra boosts the productivity of users on any desktop and dramatically reduces TCO compared to legacy platform vendors.
grommunio (formerly known as grammm) efficiently combines all requirements of modern, digital communication and collaboration.
SmarterMail is the only other email server on the market with native support for MAPI, the protocol that powers Exchange and Outlook. That means anything you can do on Exchange you can do with SmarterMail: no plug-ins and no additional software required.
OBM is a free messaging and collaboration platform useful for just a couple to many thousands of users with strong support for mobile devices.
Open Source Collaboration, providing integration with your existing Linux mailserver, native mobile phone support, Outlook "Look & Feel" webaccess and stable Outlook sharing (100% MAPI).
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