The graphic you posted could be done using a mouse (or, likely a Wacom) into a full on graphic editor, like Illustrator or Photoshop but it also could have been done much more cheaply on a phone or tablet and a stylus (or even a finger)! Even the free iOS Notes app can scribble text, though it's not as good as some of the ones you could find in the store. One of my favorites is Paper by 53.
In fact, I just created the following graphic on my iPhone using Paper and my finger in seconds (would have looked better with a stylus and more time/effort :).
