Tinderbox
By the end of page 1 of the article I was getting slightly worried - I was thinking what might be on page 2. Add cards within cards, a powerful search function, a set of 'agents' that allow you to do things like 'list all cards with 'do this next week' in the title dated a week ago', hyperlinks between cards? A powerful scripted export template?
...but no Tinderbox is safe. The only reason I would ever run Mac OS again...