Message sequence charts are our personal favorite: is some sort of weird comic strip (more like Yonokoma) in which people (or machines) are represented by vertical lines and speech bubbles by horizontal arrows. As in comic strips, you’ve to read them from the top to the bottom but sadly, in computer programming, stories aren’t very interesting nor funny.
Becoming humans
Vidiemme Brainy

Mhhh… maybe designing an interaction with sequence diagrams generates… nightmares of a possible spaghetti-software dev implementation :)

I’m strong supporter of a dialog flow scripting language that on invented by Bruce Wilcox; in that case the rule-based engine don’t oblige the conversation on a strict chronological order … ;)