I'm unsure of what you mean. Do you mean that you want something that is the equivilent of microsoft paint, if so you want seashore. But if you want something to draw on an application, which your post suggests, i have no idea what program you could use, or why you want to do that
Yea kinda like that but you can do the whole screen like draw on it circle stuff scribble stuff out on web pages or any other program or draw on the desktop.
I'm guess djstarrock wants to be able to draw on the screen, imagine keeping the desktop, with all the windows open, add a layer on top of all that to draw on.
so maybe take a screenshot (Command+Shift+3) and open it in your favourite image editor and doodle away