Paint.NET serves as both a good open source graphics editor and a test bed for new .NET functionality like the CLR add-in model. It has also been a highly coveted prize by the Mono team. On May 15, Miguel de Icaza announced that the port of Paint.NET 3.0 is functional.
This version of Paint.NET was made possible by Mono 1.2.4, which has better support for WinForms 2.0 including the ToolStrip classes. The long term plan is to incorporate the changes needed to run it on Mono back into the main Paint.NET branch. Eventually the goal is to move all platform specific code to SystemLayer.dll and simply provide a .NET and Mono version of it.
This is a major milestone for the Mono project, whose primary goal remains making it easy to develop rich GUI applications on the Linux platform.