Along with this they have done a performance analysis with numer of leading opensouce ESB's and according to the results WSO2 ESB has proven to be not only the current fastest opensource ESB but also a pioneer with the set of features it has.
Their results of the latest round of performance testing can be found in the article that published by WSO2: WSO2 ESB Performance Round 7.5.
You can download the latest WSO2 ESB 4.8.1 product here - WSO2 Enterprise Service Bus
The user guide and the documentation can be found here - WSO2ESB Documentation
