What kind of app can you use on the Mac as a sort of sketchpad?

[Flac]

I want to draw up a rough sketch of what I have in mind but if I don’t have pen and paper handy, what app could I use to draw something?

 

[aodesigns]

You could use Mischief, free from the app store.

 

[Flac]

Thank you. What is the difference between the free version and the paid version.

 

[aodesigns]

Sorry I'm not sure, I've only ever tried the free version.

 

[McGordon]

There's also Autodesk Sketchbook which is free on the Mac App Store.