Glimpse is a native macOS markdown viewer. The thing I built it around: the AI features run entirely on-device through Apple's FoundationModels (the same model behind Apple Intelligence). Summaries, key insights, an auto-glossary of jargon in whatever you're reading. Nothing leaves your machine, no API key, no account.

I read long markdown all day, mostly engineering docs and RFCs, and the existing options frustrated me. Electron apps felt slow. The fast native ones had no AI. The ones with AI wanted me to send a private spec to someone's cloud to get a summary. I wanted to open a 40-page doc and ask "what's actually new here" without it leaving my Mac.

Other things it does: double-click any rendered block to edit just that part of the source, file watching that doesn't fight you while you edit, presentation mode, KaTeX and Mermaid offline, and a QuickLook extension so .md files preview the same way in Finder.

Worth being upfront. AI needs macOS 26 because FoundationModels doesn't exist before it. The viewer and editor still work on older macOS, AI is just gated. Mac App Store only right now. 14 day free trial, then monthly or yearly subscription. I went with subscription because I want runway to keep shipping, but I'm honestly not sure it's the right model for a tool like this, so push back if it bugs you.