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There are a lot of notepad type apps out there, and pretty much all of them will do the trick. I like Floating Stickies (free - Google Play) because it's (1) free, (2) simple, (3) is only 293k, and (4) let's me put a persistent "sticky note" anywhere I want on my display. One downside to the understandable need for developers to differentiate their apps from others is that when they add features, it can get away from just being a simple, basic tool, which, when you are looking for a simple, basic tool, defeats the purpose. Floating Stickies doesn't have anywhere near the features of Evernote, but if you just want to jot a couple of words or a number down for a moment, it's great.