Clicking a button (assuming a Button cardtype?), or creating or editing a card, or a date/time arriving, or other events could trigger a script to run - e.g., to change a card's type, add _user to a Pointer included on this card, etc. Some things are probably already doable with Ruby or Script cards, but this is about Wagneerable actions.
Things we may want actions to be able to act on:
Features we may be able to reimplement this way:
+discussed in support tickets
+relevant user stories