A tool for making mockups so popular that my IE6-loving workplace has a special yammer group devoted to it.
Ooh and this one! I particularly like this one:
Honour thy father, thy mother and thy subject matter expert …
…but don’t let them anywhere near a rapid development tool. SMEs know a lot, that’s their job, but few have the gift to deconstruct their knowledge in the way needed to write with the simplicity that learners need.