Good free paint software programs include Krita, Tux Paint, HeliosPaint and Paintbrush. All of these programs need to be downloaded and installed before use. Alternatively, Artpad offers a simple online paint program directly usable via a web browser.
Krita has a wide color palette, many brush shapes, support for layering and a variety of effects. It works on Windows and Linux, and support for Mac OS is in development. Tux Paint, which features many fun special effects, is an open-source program geared toward children ages 3 to 12. It works on many platforms including Windows, Mac OS and Linux.
HeliosPaint supports many image file types and offers the tools needed for photo and icon editing. It is available for Windows, Mac OS and Linux. Paintbrush is a basic paint program for Mac OS that is similar to the original MacPaint and Windows Paint programs.