Nextcloud

Nextcloud is a self-hosted productivity and file-sync platform that lets you store, sync, and share files across devices while keeping full control of your data. At its core it provides Dropbox-style file storage with desktop, mobile, and web clients, plus secure sharing via links, passwords, and expiry dates.

Beyond file storage, Nextcloud Hub bundles a broad set of collaboration apps: calendar and contacts (CalDAV/CardDAV), Talk for chat and video calls, Mail, online document editing through Collabora or OnlyOffice, and an extensive app store for adding more functionality. It supports integration with external storage backends (S3, SMB, FTP) and identity providers via LDAP, SAML, and OAuth.

It is commonly used by individuals, teams, and organizations that want a privacy-respecting alternative to commercial cloud suites. Nextcloud is a PHP application that runs against MySQL/MariaDB or PostgreSQL and benefits from Redis for caching; a small single-user instance needs around 2GB of memory to run comfortably.