Photoflare is a cross-platform image editor with an aim to balance between powerful features and a very friendly graphical user interface. It suits a wide variety of different tasks and users who value a more nimble workflow. Features include basic image editing capabilities, paint brushes, image filters, colour adjustments and more advanced features such as Batch image processing.
Simple to use paint program like Paintbrush for Mac or classic MS Paint, but for Linux.
Krita is a free and open source painting tool designed for concept artists, illustrators, matte and texture artists, and the VFX industry.