Notepad++ (v3.1) is an Open Source source code editor with syntax highlighting. It is very light and at the same time quite powerful. It can be very handy when editing scripts on the system where no development tools are installed (see Notepad++ home page for details) especially in combination with MS CLR Debugger.
This is the screenshot of the editing "Hello World!" sample (hello.cs file).
Debugging tutorial | MS CLR Debugger