A native Markdown editor that grows into a knowledge base.

Fen is a fast, minimal Swift/SwiftUI Markdown editor for macOS and iOS — live preview, GitHub-Flavored Markdown, Mermaid diagrams, MathJax — with a roadmap toward multi-file workspaces, backlinks, and local search. Free. Open source. Apple Silicon native.

Download for macOS View source

Signed & notarized by Apple — opens without Gatekeeper warnings. macOS 15+ required.

Fen's editor and live preview, side by side, showing a Markdown document with headings, a code block, and a rendered preview pane

Why Fen?

A fen is a wetland that feeds itself — nutrient-rich, self-sustaining, always growing. That's the idea: your notes shouldn't just sit in files, they should grow into something more connected and useful over time.

⚡

Pure Swift + SwiftUI

Cross-platform core shared between macOS and iOS via FenCore. No Objective-C, no CocoaPods, no Intel-era baggage.

📝

GitHub-Flavored Markdown

Built on Apple's swift-cmark — tables, task lists, strikethrough, autolinks, and footnotes, rendered accurately.

👀

Live preview, scroll-synced

Syntax highlighting, MathJax, and Mermaid diagrams render as you type, with the preview tracking your cursor.

🧭

Apple Silicon native

Built with Swift Package Manager for the current generation of Macs — fast launch, low memory, no Rosetta.

🔓

Free and open source

MIT-licensed, with the original MacDown and Mou copyrights preserved. No account, no telemetry, no paywall.

🌱

Growing into a knowledge base

Multi-file workspaces, backlinks, local search, and a lightweight ontology layer are next on the roadmap.

Where Fen is headed

A snapshot of the full roadmap — export, a formatting toolbar, and default-editor integration are next; the knowledge suite is the long game.

Done

Full Swift/SwiftUI rewrite, Apple Silicon native

Cross-platform FenCore, GitHub-Flavored Markdown, live preview, syntax highlighting.

Export to PDF & HTML, a formatting toolbar

Paginated PDF export, self-contained HTML export, and toolbar/menu actions for common formatting.

Default .md editor integration

Set Fen as the system default for Markdown files, with a proper document icon and recent-documents support.

Knowledge suite

Multi-file workspaces, backlinks & wiki-links, local search

Open a folder as one project, link notes with [[wiki-links]], and search a workspace with an on-device index.

Knowledge suite

Ontology layer & graph view

Structured tags and note types so your notes behave like a lightweight knowledge graph, not just grep-able text.

Get involved

Fen is a small, focused project and issues, bug reports, and pull requests are all welcome.