Synapse is an Apache Incubator project that aims to create an Open Source ESB. (I came across this via Jeff Schneider, who open-sources his orchestration IDE and engine as well as his transformation stuff to add something to the mix.)

With the JBI-based alternatives ServiceMix and Celtix, there’s going to be at least three OS ESBs to choose from (strangely, with IONA involved in two of them). And I wonder whether the world even needs one … ;-)