Crossbar is an open-source software platform, hosted at https://www.crossbar.org, designed for real-time WebSocket and HTTP communication. It serves as an application router that facilitates bidirectional, distributed communication between various application components, including web and mobile clients. Crossbar supports WAMP (Web Application Messaging Protocol), offering features such as remote procedure calls and publish-and-subscribe messaging. This makes it particularly suitable for building scalable microservices and IoT applications. The platform emphasizes ease of use and flexibility, catering to both developers and businesses aiming to create robust, real-time web applications.