I've been using this engine for a few years now and I have to say I still really like it. Compared to other WF engines, this one seems to be the easiest to implement. It's a snap to enable workflows using existing business forms and processes with it. Just drop the subforms on an existing Notes form, define the workflows and the notifications and that's it! (well... almost!)
I have heavily customized its look and feel, but the actual workflow engine remains the same because it just works!
Great job!