I thought someone posted about this on vbCity Forums but I couldn't find it so I'm sharing it here.
There is free (and legal) eBook offered by Apress book publisher - Dissecting a C# Application: Inside SharpDevelop
"The developers who created SharpDevelop give you an inside track on application development with a guided tour of the source code for SharpDevelop. They will show you the most important code features and explain how you can use these techniques in your own projects. You will gain valuable experience of building an application on this scale, learning from the decisions, mistakes, problems and solutions that lead to the current version on SharpDevelop."
SharpDevelop is a free open source IDE alternative to Visual Studio .NET for C# and VB.NET, written in C# (but also without many of the wonderful features of VS.NET). It is great because you can look at the source and read in the book how they designed and implemented SharpDevelop.
If you are new to SharpDevelop, read great SharpDevelop Tutorials by vbCity member and DevCity.NET author George Poth
Click here to download the free ebook from Apress