Drawpile is a Free/Libre networked drawing program that allows multiple people to sketch on the same image simultaneously. It works with applications such as MyPaint, Krita, and GIMP. You can paint with a pixel pen, a soft brush or a watercolor brush. Brushes can be organized into presets and quick access tabs. Use a dedicated eraser tool or turn any brush into an ad hoc eraser. Both brushes and layers support various color blending modes.