iOS: Captio is a very simple, super-fast app that lets you type out a note, hit send and have an email delivered to your inbox in seconds.
Beyond that it doesn't do much else. Where Captio excels is how fast you can input a note and send it to yourself. All you need to do is enter your email address one time. Captio uses Google's mail servers to deliver the messages quickly, relieving the need for your own and and any additional setup. While Captio's primary functionality is to just send quick text notes, you also have the option of attaching a picture (whether you take it on the spot or grab an existing photo from your library). The screenshot that accompanies this post was sent to me incredibly quickly via Captio. Using iOS' normal methods not only take far longer to deliver, but are significantly more cumbersome. While this certainly isn't a use case for everyone, if you need to send photos or screenshots to yourself on a regular basis then Captio will save you quite a bit of time.
Captio is a simple yet very useful tool for when you just need to send yourself a quick reminder. It costs $1.19 and is available right now in the iTunes App Store.