Hi,
I'm currently working on a activity based workflow engine that works alot like a mix of acts_as_state_machine and An activity based Workflow Engine for PHP.
It defines a dsl that alows you to build the workflow in the model file and track each object as it goes through different states.
I have to admit that i chose to make my plugin activity based vs rule based out of ignorence, i didn't know the advanteges vs disadvantages of each system...
Once i'm done i'm hoping to release it, maybe it would help someone build a rule based workflow engine?
- Sean