Handstract is an iOS app, designed and developed by Daniel Eke.
It features a simple way to create geometric abstract images, via multitouch screens.
You can export high resolution copies of your drawings, or even lossless vector graphic PDF.
Also, this software is part of the Head Process Creative pack, check it out too.
The basic functionality centered around geometry. Draw a dot with one finger, a line with two, a triangle with three and you know the drill. Everything else will manipulate these objects. You can also change the filling, the colors, the thickness and the blending of the shapes.