Obsidian is a local-first markdown note-taking app built around backlinks and graph visualization. You write notes in markdown, link them together using wikilink syntax (note name), and Obsidian visualizes your knowledge as an interactive graph. All data is stored locally on your computer (not in the cloud). Obsidian is inspired by Zettelkasten (a note-linking methodology) and is popular for personal knowledge management, research, learning, and building a "second brain."