Introducing Screen Chomp by TechSmith. Here's a quick "what & why" video:
Warning: The video below works. I don't do anything on the screen until it goes for a bit. I describe what my screen looks like and then actually do something at 1:06. Sorry if you think it's broken. Haha!
If you want to download it, then just visit the app store and search for "Screen Chomp." You can also just go to the TechSmith website and snag it. It's free!
Have fun with it!