Nextcloud is an open-source platform for file-sharing and collaboration services. It provides a self-hosted and secure environment for managing files, calendars, contacts, tasks, and collaborating on documents. With Nextcloud, users can have control over their data and avoid relying on third-party cloud services. It offers strong security and privacy features, such as end-to-end encryption and two-factor authentication. Nextcloud is highly customizable with plugins and integrations and can be used for personal or enterprise-level collaboration.