Obsidian is a local-first, markdown-based note-taking application that stores all your data as plain text files on your device — no cloud required, no subscription, no data sent anywhere unless you choose. The graph view visualizes connections between notes as a network, revealing relationships across your knowledge base that linear notes hide. The plugin ecosystem adds AI capabilities: Smart Connections finds semantically related notes, Copilot connects to AI APIs for in-note drafting and summarization, and dozens of community plugins extend the tool in nearly any direction. The local-first approach means your data remains yours permanently. For knowledge workers who take privacy seriously, build large personal knowledge bases, or want a note tool they'll still be able to use in 20 years, Obsidian's plain text foundation and open ecosystem make it the most durable choice in the category.