GitJournal - Manage your Notes from any Git Repo.
CryptoTE - CryptoTE is a text editor with integrated strong cryptography.
Calendar Note by Enex - Calendar Note app allows users to view the calendar so they can write notes and memos according to dates to get alerts about tasks.
Notebook PEA - Protects your private notes with a password.
Category Tabs for Google Keep - Better organize your Google Keep Notes
Paranoia Text Encryption - Paranoia Text Encryption encrypts text according to a choice of strong algorithms.