Nextcloud

Nextcloud is a self hosted collaboration platform whose core is Nextcloud Files, providing file synchronisation and sharing, extended by Talk for calls and chat, Groupware for calendar, contacts and mail, and Office for document editing. The whole suite is described as Nextcloud Hub.

Self hosting is the reason organisations choose it, and the reason is usually not cost. Running the platform on infrastructure the organisation controls means file contents, user identities and access logs stay within its own legal jurisdiction and its own security perimeter. For public bodies, healthcare providers and European organisations subject to data residency requirements, that is a compliance position rather than a preference, and it is not obtainable from a hosted service whatever its certifications say.

Bundling collaboration around the files is what makes it a plausible replacement for a commercial suite rather than only a sync tool. A document can be edited, discussed in a call and shared from one platform, which is the workflow those suites provide and the reason organisations tolerate them.

The trade is operational. Someone has to run, secure, back up and upgrade the server, which is real ongoing work that a hosted service absorbs. Nextcloud is open source with paid enterprise subscriptions offering support.