The feature I think this crowd might care about: the preview live reloads when another program writes the file, not just when you type. It watches the open file with a vnode dispatch source and survives atomic saves (the write-temp-then-rename dance most editors and tools do). My own use case is working alongside coding agents that generate markdown all day (specs, handoffs, session notes) I keep Scriptum open beside the terminal and the rendered view just stays current while the file changes under it, no alt tabbing or refreshing.
The rest: SwiftUI app, KaTeX math, Mermaid diagrams, syntax-highlighted code blocks, a presentation mode that turns headings into slides, and an "Article View" reading mode tuned like an e-reader for long documents. The markdown parser is hand rolled in Swift. Honest caveat before someone finds it: the preview pane renders through WebKit (the system framework), so no, it's not 100% web-free, but there's no bundled Chromium and the app is a few MB.
Next up, since HN will ask what's coming: inline WYSIWYG editing (write in the rendered document, plain markdown stays on disk) is finished and ships in the next update, and a read-only iPhone companion that renders the same documents from iCloud Drive is in development.
No accounts, no subscription. Files stay on disk as plain text. Paid app, one-time purchase.
I'd genuinely value feedback on rendering edge cases. The parser handles GFM tables, footnotes, alerts, task lists, but markdown in the wild is endlessly creative.
If you want to try it on me: I'm giving away free copies (one per person) at https://scriptum-codes.mohamad-sakkal.workers.dev , no strings, honest feedback appreciated.