jBPM's core workflow engine is independent of http. The web component for presenting forms to a user fairly primitive and dependent on http. It would be fairly easy to replace the presentation piece with one that is not based upon html and http. I spent a couple days looking at the code and created an improved version for working in portlets using velocity. With a little more work you could create a Swing or SWT version.

I found the documentation a lacking. Once you understand the way it works, it is pretty easy to use.

If you use jBPM your workflows will be versioned. Once a workflow is initiated, that version of the definition will be used until the process completes. In general this is a good thing. However, when you have long running processes it can make updates interesting.