Obsidian is a note-taking and knowledge-base app for desktop and mobile. It stores notes on the user's device as plain-text Markdown files (Markdown is a simple text format with marks such as # for headings), so the notes stay readable without the app and work offline. Obsidian is made by a small, independent team that is supported by its users rather than investors.
Notes link to each other, a graph view shows the links, and Canvas is an unlimited board for diagrams and layouts. Through an open API, developers write plugins that change what the app does. The community directory at community.obsidian.md lists 9,587 plugins and 941 themes built by the community, in categories such as integrations, files, AI and automation; examples are Calendar, Kanban, Dataview and Excalidraw.
The app is free, also for commercial use. Obsidian earns money from optional paid services, Sync (end-to-end encrypted sync with version history) and Publish (turns notes into a website), and from optional Catalyst and Commercial licenses.