Hosting Workflow Designer in a Web Application

Hi everybody. I'm a Software Architect and I was asked to design a web application that
hosts a small workflow designer so that a power user could create its own workflow from
a small set of predefined elements, each of them corresponding to a particular business step.

Would it would be possible to build such an application using some kind of BPM framework
without having to sweat blood ? I know that the job could be done using Microsoft WF,
but unfortunately the tools I must use should be based on Java technology...

ThanKs a lot for your answers !