It’s nice to throw reference images on your work and then just drag them off the canvas to get back to later. There is a tool for creating simple animations, a multi-brush painting option, bases for multiple types of comics, and more.
Krita is an excellent, free software designed for digital painting, the customization is simple and uncomplicated, and it comes with a plethora of free. It has a nice simple ruler feature, textures, gradients, the option to add text, a complex yet useful layer system, a heap of nice pre-set tools, and special brushes that will let you create simple backgrounds. Krita delivers everything that’s missing from another free and premium painting program.