ServiceMix is an open source Enterprise Service Bus (ESB) and SOA toolkit built from the ground up on the semantics and APIs of the Java Business Integration (JBI) specification JSR 208 and released under the Apache license.
ServiceMix is lightweight and easily embeddable, has integrated Spring support and can be ran at the edge of the network (inside a client or server), as a standalone ESB provider or as a service within another ESB. You can use ServiceMix in Java SE or a Java EE application server.
ServiceMix is completely integrated into Apache Geronimo, which allows you to deploy JBI components and services directly into Geronimo. ServiceMix is being JBI certified as part of the Geronimo project.
Other J2EE application servers ServiceMix has been integrated with include JBoss with more to follow.
The aim of JBI is to allow integration components and services to be integrate in a vendor independent way, allowing users and vendors to plug and play.