Iona’s open source ESB
Heads up, Iona has open sourced their ESB, dubbed Celtix 1.0, and is a Java-based ESB (hosted by the ObjectWeb Consortium). Apparently Celtix doesn’t rely on a central hub, so it’s more distributed than most ESBs. It should run with any Java Business Integration container and features an implementation of the JAX-WS (Java API for XML Web Services) specification for building Web services-based Java applications. SOAP is supposed to be supported natively as well as multiple transports such as JMS, XML, and HTTP.
I’ve heard Celtix is best for small non mission-critical applications, but that it doesn’t rely on a central hub. Other open source ESB’s include SymphonySoft’s Mule and LogicBlaze’s ServiceMix.