Obsidian is a note-taking app that stores your notes locally as plain Markdown files. It suits anyone building a personal knowledge base, journal, or project notes they want to keep in an open format.

Key features:

Link notes to each other to build your own personal wiki.
Visualize the relationships between notes in an interactive graph.
Research, brainstorm, and lay out ideas on an infinite Canvas.
Extend the app with thousands of community plugins and themes, such as Calendar, Kanban, Dataview, and Tasks.
Work offline, with notes stored privately on your device.
Sync notes across devices with end-to-end encryption and version history through the optional Sync service.
Publish notes as a website, wiki, or digital garden with the optional Publish service.

Obsidian is free with no sign-up required and collects no telemetry. Sync costs $4 per user per month billed annually ($5 monthly), and Publish costs $8 per site per month billed annually ($10 monthly). An optional $25 Catalyst license gives early access to betas, and a $50 per user per year commercial license is encouraged but not required for work use.