"It won't be the only open source BPEL server available. Orbeon Inc., a systems integrator in Mountain View, California, released the source code for its BPEL server a few weeks ago, along with several other components that comprise the Orbeon Integration Suite."
Unfortunately that's not quite the case... Orbeon did found and seed the Open Integration Suite project with a contribution of it's OXF product line, but it will be sourcing other complimentary components, including a BPEL Server, from other open source projects. The good news is that eMaxx's is now a candidate for inclusion in the suite! (Disclaimer: I am currently on Orbeon's board of advisors.)