My favorite note-taking app. Simplenote is a free, open-source service that provides a text editor that synchronizes notes between any type of device: Linux, Windows, macOS, iOS, Android, and any web browser. Notes are saved locally on the app for use offline, but will update and sync across devices when connected to the internet. Simplenote is made by Automattic, the company behind WordPress with a strong track record of promoting open-source software.
Simplenote is, as its name suggests, very simple. It does not use folders, however notes can be assigned a tag or searched. Notes are sorted by date and individual notes can be pinned at the top of the list. It only accepts text input; the notes cannot be formatted as in a word processor, and it does not accept images. I use Simplenote to keep track of my many projects and jot down ideas throughout the day.