When you want to check a script for errors, and you’re just carrying your thumb-drive this tool might be handy. PrimalPad is a single file, color coding editor for VBScript, JScript, HTML and PowerShell. It supports line numbers and a multi-tabbed environment. No installation required, just one single executable file.
Another free editor I reguly use is Notepad++ Portable, version 5.3.1 has been released recently. It's the handy Notepad++ text editor packaged as a portable app so you can do your development on the go. It has all the same great features of Notepad++ including support for multiple languages and an extensive plugin system, but there's nothing to install. This release updates Notepad++ to 5.3.1 and fixes portablization of settings. It's packaged in PortableApps.com Format so it can easily integrate with the PortableApps.com Suite. And it's open source and completely free.