NextCloud
Nextcloud is a big part of why I can use Cloudready machine for much of the time. It provides file sharing services, webmail, contacts and calendar sharing, password management, tasks, notes, bookmarks, and more. It has a load of Android apps for sharing, automatically uploading photos, syncing files, calendars and contact lists, task management .... just some of the stuff I use. There are loads of plugins for things like video conferencing, online chat, Solr searches …
Nextcloud can be installed on your own servers, on a serviced providers servers or by Nextcloud themselves. This keeps all your data under your control.
By strictly adhering to open standards, Nextcloud is compatible with most other software. Files can be accessed with WebDAV, calendars and contacts can be shared with CalDAV and CardDAV.