Obsidian stores everything as plain markdown files in a local vault — no proprietary format, no lock-in, just folders and files you own. The killer feature is bidirectional linking: notes reference each other and the graph view shows how ideas connect. I use it for the bee-hub vault itself, long-form notes, and anything I want to keep permanently searchable. The plugin ecosystem is enormous, covering everything from kanban boards to Dataview queries that turn your notes into a database. Syncs across devices via Obsidian Sync or a folder-based solution like Resilio.