I am a huge fan of Scrivener, the biggest thing for writers since...well, since ever! I am always discovering things I didn't know, and I was so excited to find that Scrivener has a Scratch Pad that is available across the board. Meaning, if you are in one project and you think of something for another project (which I do often), you can simply pull up the Scratch Pad and type in your note, and then later, when you switch to the other project, open up Scratch Pad and there it is! Meaning, you don't have to go out of one project to put in a note or an idea for another. Pretty cool, huh? To try it out, while in a Scrivener file, just go up to the top menu bar where you see the word "Window" - click on that and go down to "Show Scratch Pad".
If you haven't tried Scrivener, you can go here and download a free trial. You'll love it!