I've used Drawpile entirely for this drawing. It's a nice program, but I wish they had a few more tools like Magic Wand Tool, which would be helpful.
It's weird that I actually can't find the name of it in english, but we call it "Torta Holandesa" over here. It's "Dutch Pie" if literally translated. A picture: http://bit.ly/1qgomY3
