CS-Script
CS-Script is a free and open-source scripting platform that enables creating scripts in ECMA-compliant C# syntax. These scripts have access to .NET Framework or Mono APIs.
CS-Script offers standalone script execution as well as hosting the script engine from CLR apps. A newer edition of this product, called CS-Script.Core works with .NET.
Existing .NET development tools (e.g. Visual Studio and Sharp Develop) can be used, allowing editing and debugging scripts within traditional .NET-aware development environments. Additionally, CS-Script support can be added to Notepad++ or Visual Studio Code via plugins.[2][3]
FlashDevelop uses CS-Script as its internal scripting engine.[4]