Something that didn't occur to me until today. CircleDock is open source and C# based. At least the most recent version is. This might be something fun I can mess with in my off time. I emphasize might because I am very bad at sticking with projects for any amount of actual time.
EDIT: Ok, so based on my research, something weird happened wtih CircleDock. The short version is that the .NET version was prototyped by one person before another developer picked up the torch. Then they basically deleted all of their work because they felt trapped by the GPL license that they had inherited. To make a long story short, the version of CircleDock you can find on SourceForge is nowhere near the most recent version of the program. Furthermore, the source code is not the same version as the compiled version of the code. There is some basic functionality missing there. Trying to make it better based on what is already in source code form would be quite a challenge.