Windows: Scratchpad is a simple little app that sits out of your way until you need it, providing you a quick place to jot down any and all notes with just a few keystrokes.
Scratchpad is simple: Press Win+S to bring up your pad, jot down your notes, then press Win+S to dismiss it again. It’s portable, so you can stick it anywhere on your computer, and even give it a template so it starts off with the same skeleton note every time you start it up. You can run it as a standalone app or put it into one of your existing AutoHotkey scripts.
Scratchpad is a free download for Windows only.