Here is a Mono CsharpRepl which is what you are looking for.
This documents the features available
in the C# interactive shell that is
part of Mono's C# compiler. An
interactive shell is usually referred
to as a read eval print loop or repl.
The C# interactive shell is built on
top of the Mono.CSharp
(http:/monodoc/N:Mono.CSharp) library,
a library that provides a C# compiler
service that can be used to evaluate
expressions and statements on-the-fly.
Like others noted, Mono's CSharpRepl is probably the right answer. However, if you're not fixed to C#, then PowerShell is a pretty nice environment of playing around with .NET. I frequently use it to test regular expressions, format strings, etc. All the kinds of stuff you have ConsoleProject163 lying around for :)
Then open your terminal (CMD, PowerShell, Windows Terminal) and type csi to run C Sharp Interactive.
You'll get something like this:
PS C:\> csi
Microsoft (R) Visual C# Interactive Compiler version 2.6.1.62414
Copyright (C) Microsoft Corporation. All rights reserved.
Type "#help" for more information.
> var list = new List<int>{ 1, 2, 3, 4 };
> list // You don't need to call Console.WriteLine() to see values
List<int>(4) { 1, 2, 3, 4 }
> // You can keep adding lines as needed
If you are looking for a simple web based environment to crank out some C# code try coderpad.io Not sure if you can add libraries n' all but its a quick and simple solution if you are just interested in testing out several commands
With Roslyn CTP there now is a full C# interactive window from Microsoft direct in Visual Studio!!
Works great! So far runs all my libraries.
After install: Invoking View -> Other Windows -> C# Interactive from the menu.
I think CShell would be a nice contribution to answers given here.
It provides code completion enabled REPL command window as well as a lightweight workspace management tools to include some scratch files and library references.