Inkscape is a free and open-source vector art editor that uses Scalable Vector Graphics (SVG), allowing your artwork to be scaled to any size without losing quality.
MediBang Paint is a versatile and free digital painting and manga creation software available on multiple platforms, including Windows, Mac, iPad, iPhone, and Android.
GIMP is a free and open-source raster graphics editor used for a variety of graphics editing tasks such as photo retouching, image composition, image authoring, and even drawing and painting.
MyPaint is a free and open source digital painting program developed by Martin Renold that includes an unlimited canvas, a custom procedural brush engine, and a diverse set of color wheels.
FireAlpaca is a free digital painting software designed for both Windows and Mac users, featuring regularly updated brushes, comic panels, animation tools, mesh transform, 3D perspective tool, and more.