Obsidian

Obsidian is a local-first note-taking and personal knowledge management app built around storing notes as plain markdown files on the user's own device rather than in a proprietary cloud database. Notes remain accessible offline, are private by design — the company states no one else can read them, not even Obsidian itself — and use open file formats specifically so a user's notes are never locked into the app long-term. The core app is free, with thousands of community plugins and themes available to customize how it works, and optional paid add-ons (Sync, Publish) plus an Enterprise tier for teams that want managed deployment and support.