"One alternative for commercial ESB could be a reliable, open source ESB. In the market, there are several open source products available that compete not only within the open source community but also with commercial ones. Mule ESB is one of the most prominent ESB products in the open source category and also claims to be the most used in the open source ESB product category.
"Mule is open source, well documented, tried and tested. It is vendor neutral and can be plugged into any number of vendor implementations. It comes with built-in support for lots of protocols such as HTTP, JMS, SOAP, SMTP and many more. With the robust architecture that Mule has, it supports seamless integration of applications of different natures.
"Different real world applications use different protocols and message formats. This can make the application integration really difficult. In order to solve this integration problem, Mule provides a framework that converts data into messages that get routed to other applications and the entire thing is controlled through configurations. The real advantage of this framework is that it separates the business logic (usually implemented by enterprises) from the messaging logic that is responsible for routing messages between applications. When the destination application needs a different message format, Mule uses constructs called "Transformations" that transforms the message from source format to destination format."
