Apache Synapse is an extremely lightweight and easy-to-use Open Source Enterprise Service Bus (ESB) available under the Apache Software License v2.0. Apache Synapse graduated from the Apache Incubator on the 2nd of January 2007, and was accepted as a sub-project of the Apache Web Services project. In December 2007, Apache Synapse became a top level project (TLP) of the Apache Software Foundation
Documentation for the 1.1.1 release: