Obsidian

Obsidian is the private and flexible note‑taking app that adapts to the way you think. Obsidian stores notes on your device, so you can access them quickly, even offline. No one else can read them, not even us. With hundreds of plugins and themes, you can shape Obsidian to fit your way of thinking. Obsidian uses open, non-proprietary files, so you're never locked in, and can preserve your data for the long term.