I spend a fair amount of time writing code in C#, which I enjoy. I occasionally wish I could use C# inside other applications.
I call it QueryStorm. I started working on it way back in 2014. It originally had just SQL support, and I’ve continued working on it ever since, gradually adding support for C# scripting, custom C#/Excel functions, NuGet support, a debugger, and even an app store!
QueryStorm uses AvalonEdit as its code editor. AvalonEdit is a fancy textbox that can show text with rich formatting, but it doesn’t know anything about the C# language and its syntax. It needs to be told where symbols and errors are located in the text (so it can highlight them), which autocomplete options to offer, etc.