Last but not least, I want to mention another one I found. :3 It's called Paint Online - Sketch & Paint!. The features are more advanced in it than those in Paint, btw. I think this is worth trying out too! I made an example picture below, but to see the actual thing, click here.
Okay, so I know there are even more advanced art editors, like Photoshop, GIMP, Krita, Manga Studio, SketchBook, and so on, but I think these are pretty cool too. :D (Especially if you use Windows 8.1 RT that won't let you download anything apart from apps from the store >.<)