Ink for iOS
I do a fair amount of sketching on my iPad mini. As I'm not doing so for artistic reasons (I'm usually just sketching out a diagram or layout), many of the drawing apps on iOS are overkill for my needs.
Enter Ink. The new free iOS app from Minimal Tools offers only one color and weight of ink, on a white canvas. With simple export options, it's easy to save and share my doodles or diagrams easily. Go check it out on the App Store.