Nextcloud is a self-hostable, open-source, cloud platform. By default it includes tools like file sharing (with accompanying mobile apps), calendars, and contacts that can replace commercial services like Google. It also has an App Store featuring a wide range of collaboration and productivity tools.
This is a powerful, multi-purpose tool for bringing many of the features of cloud environments under complete user control, free of surveillance or dependency. The usability of the particular apps varies, so testing beforehand is recommended. Depending on how it is deployed, also, Nextcloud requires some server administration skills.
Collaborative document editing
Nextcloud can integrate with the collaborative editing apps Collabora and OnlyOffice. The native format is Open Document Format, and it supports word processing, spreadsheet, and presentation files.
Plain text and Markdown files can also be easily edited with Nextcloud add-on apps, as well as Etherpads.
Group file storage
Admins can manage access for a group of users, such as a class. The interface is similar to Google Docs or Dropbox.
Desktop and mobile clients allow users to sync documents to local computers.