That's the name of it: Desktastic, from Panic, Inc.
It's a fun and easy little program for the Mac that turns your desktop into a piece of scratch paper. Draw, type or doodle anywhere on the desktop that you like, any time inspiration strikes. You can be silly, or (as happens all the time with me) you can jot down a phone number, a name, or a sentence fragment.
You can use the whole desktop, a piece of the desktop, or you can write over your application windows if you want to make notes on top of things. Then you can save the results.
You can use a tablet, the keyboard, even your finger. It's a simple but very useful piece of software, and it's cheap to boot. Check it out.