CryptoTE - CryptoTE is a text editor with integrated strong cryptography.
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.
Daybreak - An intelligent to-do app that learns when to remind you
Standard Notes - A safe place for your notes, thoughts, and life's work
Notebook PEA - Protects your private notes with a password.