Mac: Launchwrite is a simple app that stores notes, thoughts or whatever other text you want in a notepad overlay on your screen. You call it up with a keyboard shortcut (Command+Shift+L), start typing, and put it away when you're done.
Watch the video above for a demo.
The app is very simple, so there's little more to it than that. It works a lot like Launchpad — the iOS-esque app launch built into Mac OS X — in that it blurs out your desktop to provide you with a dedicated space. You can set the text to white, black or various shades of grey so it shows up well on your background. From there you just type what you want to type and hide Launchwrite when you're done.
When Mac OS X 10.8 is released, you'll be able to use it to dictate notes as well. Launchwrite was not designed to replace your word processor or database of many notes, but mainly to be a quick sketchpad for things you want to remember, ideas you have, or any other kind of text you just need to jot down quickly. It won't be an app for everyone, but it's useful for those of us who need a quickly-accessible and dedicated space to hold our ideas.
Launchwrite ($1.99) [Mac App Store]