https://fuqua.io/CSharpRepl/

csharprepl
GitHub 

A cross-platform command-line C# REPL

Explore the language, libraries and nuget packages interactively

dotnet tool install -g csharprepl

Experiment with C# and .NET APIs

Quickly try out C# syntax and .NET APIs, without needing to litter
your filesystem with testing projects. Command-line autocompletion
helps you find answers fast.

[experiment]

Install NuGet packages

Use the #r command to reference NuGet packages; the autocompletion
window shows relevant method/class documentation.

[nuget]

Navigate to source code

Ever find yourself Googling for a library's source code? For NuGet
packages and assemblies that support SourceLink, browse their
original source code by simply pressing F12.

[sourcelink]

Reference your existing projects

The #r command can also reference assemblies by name and filepath, as
well as your own .csproj and .sln files.

[reference]

Dive into the IL code

Curious how a feature in C# works? Press F9 to view the IL code of
any statement or expression you've typed.

[intermedia]

Free and Open Source. Install it now by running:

dotnet tool install -g csharprepl

https://github.com/waf/CSharpRepl