Let's say you are building a Python-based web app that requires some workflow management such as that in jBPM or Windows Workflow Foundation. Is there a library that offers this in the Python world?
Oh yes, tons. But most of them depend on a specific framework. DCWorkflow is integrated with Zopes CMF, for example. hurry.workflow is for Zope 3, etc. SpiffWorkflow presumes sql-alchemy, etc. This is because you need to have something to apply the workflow to, and that means you need to make some basic assumptions on the objects you use.
Hurry.workflow is probably one of the more independent ones, but it still assumes both that you use the Persistence library (and therefore in practice ZODB), and zope3's security model.
So you probably need to expand a bit on your requirements here...