Obsidian

Obsidian is a powerful, local-first knowledge management and note-taking app that uses plain Markdown files stored on your device. Launched in 2020, Obsidian quickly attracted a passionate community of knowledge workers, researchers, writers, and developers who value privacy, data ownership, and flexibility. Its defining feature is bidirectional linking — every note can link to and be linked from any other note, creating a personal knowledge graph that you can visualize in the Graph View. Obsidian's plugin ecosystem (with over 1,000 community plugins) makes it infinitely customizable, from spaced repetition flashcards to Kanban boards to daily journal templates. The core app is free and works entirely offline, syncing via your own cloud storage or Obsidian Sync. Unlike Notion or Confluence, there's no vendor lock-in — your notes are plain Markdown files that work with any text editor forever. Obsidian is particularly popular in the 'second brain' and personal knowledge management (PKM) community. Premium features like Sync ($4/month) and Publish ($8/month) are opt-in additions.