SharpDevelop VS ILSpy

SharpDevelop is a dead project, https://github.com/icsharpcode/SharpDevelop/issues/799

SharpDevelop and MonoDevelop are both dead and focused for devs which gives them different priority than apps targeted at non-devs, but they show how to put together seriously complex apps, and they're the ancestor of the Visual Studio for Mac.

You should try SharpTreeview. Haven’t had any issues with it for large treeviews

Yes

I've also used this for its WPF editor https://github.com/icsharpcode/SharpDevelop but I dont know if it does WinForm

First, go grab this: https://github.com/icsharpcode/ILSpy. It's a decompiler that will break Rust down. Hope you like C#.

If its a C#/.NET exe you can use ILSpy to get the source code https://github.com/icsharpcode/ILSpy

Well, it might not be exactly what you're asking for, but ILSpy lets you choose what version of C# you wish to decompile an assembly to. This is great for learning how a specific feature used to be coded in C# prior to some new syntax/compiler feature being added.

You will thoroughly enjoy this, then.

I've only used their GUI frontend myself, but ILSpy is also available as a library and command line tool.

As you can see IL code is not exactly human readable, and it's also quite verbose. If you want to have an idea of how your code looks like in IL you can use a decompiler tool such as JustDecompile or ILSpy.

Take a random piece of C# software, run it through ILSpy, and be amazed at the results.