C# IntelliSense plugin for Notepad++ (CSScriptNpp)

This plugin allows convenient editing and execution of the C# code (scripts). It also allows the usual C# IntelliSense and project management tasks to be performed in a way very similar to the MS Visual Studio.
In addition to this, it provides generic debugging functionality (with the integrated Managed Debugger) as well as the ability to prepare C# scripts for the deployment packages (script+engine or self-contained executable).
Typically user opens the C# file with Notepad++ and after presses 'Load' button on the CS-Script toolbar the all features can be accessed through two Notepad++ dockable panels Project and Output panel.

Source: csscriptnpp.codeplex.com