"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."