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Inkscape (not too versed)

Having a download and peek, Inkscape is a free Illustrator alternative. I believe the main idea behind those types of apps is that you can attribute those point curves to every object in a drawing thus giving full control to rearrange or manipulate them anytime you like, especially if they are on top of one another. 

This can be somewhat done with Photoshop, PSP, GIMP, POS PRO layers but not as exact as with Illustrator type software.

Although actual free drawing or painting with something like this looks impossible so I think, don't quote me on this because I'm not too versed either, I think you place down a pointed shape on your document and import your free hand drawn and painted stuff into that shape so that you can also have free control over moving and resizing those images as well.

Art Rage appears to be more of flexible free-hand-drawer for WACOM fun:
http://www.artrage.com/