If your device is rooted, it can be any of the following stuff – launch app, change/reset resolution, dial contact number, press a navigation key, show tasks or show recent apps. Very handy!
Setting up a gesture shortcut is pretty much a two-tap process, it couldn’t possibly be any simpler. Additionally, the dot can be dragged anywhere on your screen and it won’t disappear when you start doing other activities. But, should you need to get rid of it temporarily, just long-press the dot and it will retreat inside the notification bar. You can pull it back out of hiding anytime, or enable and disable it for good from the app itself.
NOMone Gesture Dotty is free, with optional in-app purchases.