Another open source minimal workflow engine. It could be described as a state machine. It requires a lot of coding to implement real business process but can be useful in simple cases
The Taverna project aims to provide a language and software tools to facilitate easy use of workflow and distributed compute technology within the eScience community
E. Sekerinski, and R. Zurob. &\#171;UML&\#187; '01: Proceedings of the 4th International Conference on The Unified Modeling Language, Modeling Languages, Concepts, and Tools, page 376--390. London, UK, Springer-Verlag, (2001)