The GNU Image Manipulation Program, or GIMP, is a raster graphics editor used to process digital graphics and photographs. (GPL)

Krita is a painting and image editing application for KOffice. (GPL)

mtPaint is a painting program designed for creating icons and pixel-based artwork. (GPL)

MyPaint is a fast and easy painting application. It lets you focus on the art instead of the program. (GPL)

Nathive is a libre software image editor, similar to Adobe Photoshop, Corel Photo-Paint or GIMP, but focused on usability, logic and providing a smooth learning curve for everyone. (GPL)

Paint.NET is an open source, raster graphics editing program for Windows, developed on the .NET Framework. (MIT)

Pinta is a drawing/editing program modeled after Paint.NET. It's goal is to provide a simplified alternative to GIMP for casual users. (MIT)

Pixen is an innovative graphics editor for the Mac. It's designed from top to bottom for pixel artists. (MIT)

Tux Paint is a free, award-winning drawing program for children ages 3 to 12. (GPL)