Over the past year I have been working with a group of software engineers to create a simple, fast, yet powerful App for Microsoft's Surface. Sketchable is the result. It was just released and available to the public in the last couple weeks. Not only does the app work on the Surface but on any machine running Windows 8.1. It will run great on a desktop or laptop.
This is not a full blown painting program and was not meant to be that but it is a great sketching and doodling program. The program is extremely fast. There is no lag to the brushes at all. At first glance the brushes are simple but dig a little deeper and you can change almost any attribute you can think of. Color picking is simple.
I do like the journal or sketchbook opening interface. Having multiple sketchbooks is how I work in real life anyway.
A cool feature is starting the camera, taking a shot, and then being able to annotate the image or even paint over the whole thing.
It is very simple to start using and would be great for just jotting random thoughts down as well as drawing. I would recommend taking a look at it if you want something simple to use but enough options and power to keep you happy. The home page is; http://www.siliconbenders.com/
Here are a couple of sketches I created using beta versions.