Nextcloud

Nextcloud server turns a Linux box you own into the storage backend most people rent from Google or Dropbox. Install it, point a browser or the desktop/mobile client at it, and files start syncing across every device you own — no vendor, no subscription, no third party reading your data. The core repo ships file storage and sync, but the real draw is the app ecosystem: Calendar, Contacts, Mail, and Talk (Nextcloud's video-chat app) all bolt on through the same interface, turning a file server into something closer to a self-hosted Google Workspace. Sharing works the way you'd expect — link a file, set permissions, done. Two-factor auth and a HackerOne bounty program back the security side. Getting it running from source means initializing git submodules for third-party components — a step that trips up first-time contributors — and the project is explicit that checkouts of master aren't meant for production. Most people will want a release tarball, a Docker appliance, or a hosting provider instead of building from the repo directly.