Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.
Calmly Writer - Distraction-free text editor for Mac, Windows, Linux and ChromeOS.
Boostnote - Boostnote is an open-source note-taking app.
Writebox - Writebox is a simple and distraction-free text editor for Chrome and iPhone/iPad.
Standard Notes - A safe place for your notes, thoughts, and life's work
Stashany - Online notepad for developers