Paint.NET has a neat plugin called CodeLab that ... well, let me quote:
Here's an "effect" that Tom wrote. Basically what it does is let you write code that is compiled on the fly and that is then executed in the Paint.NET effect engine. This is the same plugin that we made available for Paint.NET v2.1, but it has been updated to work with Paint.NET v2.6. With this you can implement almost any type of effect you want if you have the programming and mathematical talent to do so. This plugin works by presenting you with a simple text editor that you can use to type in C# code that is then compiled and executed (rendered) as soon as you stop typing.
Please note that this is experimental technology and is not meant to provide a robust development environment. It is perfect for rapid prototyping and very useful for educational purposes including teaching computer graphics.
This plugin especially benefits from Paint.NET's extensive multiprocessor and multicore support. For instance, if you are interested in rendering high resolution fractals on an expensive workstation, this is the way to do it! The code you write is automatically multithreaded and the workload is spread across multiple CPU's resulting in near linear performance scaling (4 CPU's = almost 4x faster).
There are several code samples included with the plugin to get you started. Anyway, I've been having a lot of fun messing around with this and thought you guys might enjoy it.
