Tomboy - Apps/Tomboy - GNOME Wiki!
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.
Turtl - The secure, collaborative notebook
Boostnote - Boostnote is an open-source note-taking app.
Omni Notes - Note taking open-source application aimed to have both a simple interface but keeping smart behavior
Day One - A simple journal application for the Mac, iPhone, and iPad. AboutTo learn more about Day One, see these two excellent reviews . PublishPublish is not available in Day One 2.