Jointly developed by Washington State University and Microsoft, Paint.net is intended to be a replacement for the free MS Paint software provided with all Windows operating systems.
It offers many of the powerful features found in commercial editors, including the ability to work on multiple layers, full transparent PNG support, unlimited history, and a plethora of visual effects.
An interesting feature is the way each tool window becomes transparent when covering the image. This enables better implementation of effects and is something the big image editors are currently lacking.
Features include a multi-document, tab-based interface, so you can open and edit more than one image. An improved and more powerful toolbar and user-definable colour palette are some of the other highlights.