Cloud storage services are great for ad-hoc backups, accessing key documents from anywhere and easily sharing files with family and friends, but they also have a fundamental issue: you're giving all your files to another company, trusting that they'll treat them properly, and (with the likes of Google and Microsoft) hoping that they won't use your activities to build up an even larger database on you than they have already.
Nextcloud is a free open-source cloud storage platform which you can host yourself, using your own domain and almost any web hosting plan (even many of the cheapest.) There's no need to create an account or hand over any personal or payment data (other than for the web hosting plan, anyway), and no restrictions on sharing the service with friends, colleagues, or anyone else.
