RethinkDB is an open-source, distributed NoSQL database designed for real-time applications. It allows developers to build applications that can instantly respond to changes in data with push-based updates. Unlike traditional databases, RethinkDB provides built-in support for real-time feeds, making it ideal for building collaborative apps, dashboards, and messaging platforms. It features a flexible query language and a powerful web interface for managing and monitoring databases. RethinkDB's architecture is optimized for horizontal scalability and high availability.