While working on our Web Services Substrate, we did a lot of looking at
the coming BPEL standard.  While it doesn’t do everything that we
wanted, it provides some powerful functionality, and will only evolve
to be better and better.  I happened to stumble on this Open
Source project providing a BPEL engine … I’m going to go take a look
at it …

ActiveBPEL 0.9.2. An engine that executes BPEL processes. [freshmeat.net]