Simplenote from Automatic Inc is a note taking app that runs on multiple platforms. This is not the only note taking app of course, but what makes this different is that it syncs your notes across various devices. So once you enter your notes on mobile or desktop it is automatically synced with your tablet, smartphone, laptop etc.
At the left of the home screen are your most recent notes. At the top is a search bar where you can look for other notes you made. The empty space on the right is where you type your notes. There are some slight differences across platforms but the general functionality is the same.
You write notes as Markdown or plain text, and tapping the toggle button lets you preview the markdown. You can type short notes or write them down on different devices as the sync works well here. You could jot a few quick notes on your phone for instance and write in more detail on your laptop later.
Simplenote has a character and word counter in the menu. There is no spell checker but that is not a big deal since this is just for note taking anyway. If you decide to publish your notes, a link will be provided so you can share it with others online.
Simplenote also has automatic versioning that allows you to go back to previous version of your notes. Suppose you wrote a detailed note, edited it heavily and decided you want older version back. Just click or tap the clock icon and move the slider to see the older version of your notes.