RoslynPad is an open-source code editor for C# scripts (.csx files), built using Roslyn and AvalonEdit. Some of its features include code completion, signature help, diagnostics (squiggles), code actions (bulbs) and NuGet support.
Roslynpad is a simple cross-platform C# editor based on Roslyn and AvalonEdit.
You might also take a look at linqpad