Open Source NAS
A network-attached storage box is where a household's photos and a team's working files quietly accumulate into something irreplaceable, which makes the operating system running it a long-term commitment, not a convenience - you are trusting it with the one copy you cannot regenerate. The open source NAS systems here put that storage on hardware you own and an OS you can inspect, so your files stay reachable on your own terms instead of behind a cloud subscription that can lapse.
Copyparty
Portable file server with resumable uploads, WebDAV, SFTP, FTP, TFTP, and browser access
CasaOS
Personal cloud system for home servers with an app store and drive management
Kopia
Cross-platform backup and restore tool with encrypted snapshots, deduplication, and CLI plus GUI
OpenMediaVault
Debian-based network attached storage with a plugin framework for home and small offices
TrueNAS
ZFS-based storage platform with file, block, and object services across CORE, Enterprise, and SCALE
Rockstor
Linux and BTRFS based NAS appliance with Docker apps and RESTful APIs