Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.
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.
GitJournal - Manage your Notes from any Git Repo.
wreeto - A simple workspace to help you focus.
Quillnote - Take beautiful markdown notes and stay organized with task lists.
Notebook PEA - Protects your private notes with a password.