SketchBook Ink is made by Autodesk, the same developer that makes SketchBook Pro. This is a really fun program that mimics different types of ink. It has seven different ink brushes and two erasers. It supports layers and you can import and export images. The ink pens are really smooth and mimic sumi brushes, dip pens, fountain pens, and ballpoint pens. I like to use this app to make pen and ink drawings. I've also seen several people use this app for drawing comics. You can export high resolution images, 12,800 pixels by 8,000 pixels, from this app and PSD files up to 101.5 MBs. Here is an example of a tatoo design I drew from the android app How to Draw Art Lessons. I also like to use it with Auryn Ink, a watercolor painting app.
Here is the UI for SketchBook Ink.