Pinta

Pinta is an image-editing tool along the lines of Adobe Photoshop and Gimp that allows you to create drawings from scratch as well as perform complex edits to already-existing photographs.

It puts all the common graphic editing and design tools at your disposal: paintbrush, paint can, cloning stamp, gradient, different selection types, etc.

The program includes an accessible, familiar layer system that won't be new to anyone who has ever used the programs mentioned before, as well as a complete history function that you can use to easily undo actions.

Other options allow you to apply artistic effects, blur, and render.

Pinta is an excellent option among the countless image editors out there. One huge plus? It's completely free.