BuildDecayChronograph, an object that shows you how long it's been since a given SWF was last built, and a quick visual indicator from green to red of how fresh it is (for me, 5 minutes). The only requirement is that the given SWF was compiled with
addChild(new BuildDecayChronograph(5*60, 'engine'));
Download from GitHub.
This could not have been done without the brilliantly hacky