Nextcloud is an open-source file sync and share platform that provides an alternative to proprietary services like Dropbox, Google Drive, and Office 365. It allows users to have their own self-hosted solution that is 100% open source and avoids vendor lock-in. Nextcloud uses a distributed and federated architecture, supports security features like end-to-end encryption, and offers enhanced collaboration tools like video calling, chat, and screen sharing. It has a growing business providing commercial support and services to enterprises and individuals using the Nextcloud platform.