A few minutes ago, Asanka Abeysinghe the Director of Solutions Architecture of WSO2 claimed that the WSO2 ESB supports "Zero Copy", at the WSO2Con held in Colombo, 14th September 2010
However, this statement is false, and can be easily proved by just looking at the implementation source code of the BinaryRelayBuilder, which copies the complete input stream into a byte in Heap memory via traditional CPU copying into user space.
In-fact, when WSO2 announced this "Binary Relay" in December 2009, even the author of this "feature" did not state that its anything near "Zero Copy". Even a search on Google for WSO2 and Zero copy returns no results!
"Zero-copy" describes computer operations in which the CPU does not perform the task of copying data from one memory area to another." - Wikipedia
The AdroitLogic UltraESB is the FIRST and still the ONLY Open Source ESB (or most possibly "the only ESB") that supports True Zero-Copy proxying.
Thats why its the fastest ESB out there!