Mule ESB is a lightweight, open-source integration framework that allows for quick and easy connection of applications to enable data exchange regardless of technology. It uses a service-oriented architecture and can integrate applications using technologies like JMS, web services, JDBC, and HTTP. Mule ESB is highly scalable and vendor-neutral, allowing components from any vendor to be used without lock-in. It can deploy in various topologies to decrease time to market and increase productivity for secure, scalable applications.