Open Source is associated with most software products nowaday and middleware are no exceptions.
As a middleware user, how does open source benefit you? .
1. Being open source means, you do not have to buy a commercial license to use the software.
2. There will be regular updates, which means, you can keep your deployment up to date with respect to security flows etc.
3. Open source means, there is a definite cost advantage, when it comes to total cost of ownership of a software product.
However, most open source middleware products do not come as a fully open source. Sometimes, there is an open source community edition and an enterprise edition and so forth. Hence, WSO2 ESB is one of the truly open source Enterprise Service Bus product.
Learn more about the open source nature of WSO2 ESB from "THE OPEN SOURCE ESB" article.