Krita

Krita is a free and open source digital painting application built for creating artwork from start to finish. It is aimed at professionals and serious hobbyists who want a dedicated canvas rather than a general-purpose image editor.

Artists use it for comic book pages, illustrations, concept art, matte painting, texture painting, and digital VFX work. A deep brush engine, layers, masks, and color management give you the control to take a piece all the way from blank canvas to finished render.

Krita runs on Windows, macOS, and Linux and is developed as part of the KDE community. It is free software under the GNU General Public License version 3.