I'm currently working on a activity based workflow engine that works
alot like a mix of acts_as_state_machine and

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