Nextcloud

Commercial cloud storage has three chronic problems: capacity billed monthly, throttling for non-subscribers, and files that can vanish to content scanning. Nextcloud's answer is to move the whole service onto your own hardware — capacity equals your disk, speed equals your network, and nobody scans your files. 36,417 stars, AGPL-3.0, and one of the most mature projects in self-hosting.

It is far more than a drive. After the core install, an app store offers hundreds of official and community apps: calendar and contacts (which your phone's built-in apps can subscribe to directly), tasks, notes, kanban boards, a password vault, a mail client — and with Collabora or ONLYOFFICE attached, real-time collaborative editing of Word and Excel documents in the browser. Plenty of small teams use it to replace an entire online office suite.

Desktop clients cover Windows, macOS and Linux and behave like Dropbox, including selective sync and virtual files that occupy no space until opened. Mobile apps handle automatic photo backup.

Be clear about the cost: you need a machine that stays on. An old laptop, a NAS, a Raspberry Pi or a cheap cloud VM all work, and official Docker images plus the all-in-one AIO deployment make setup manageable — but updates, backups and HTTPS certificates become your job. It is also a PHP application, so on very modest hardware (an early Raspberry Pi, say) the web interface feels sluggish; using PostgreSQL instead of SQLite and adding Redis caching helps a great deal.

If you only want photo backup, Immich is more focused and faster; if you only want password sync, Vaultwarden is lighter. Nextcloud is the "one machine handles everything" option.