He says it's a custom site: https://notes.andymatuschak.org/About_these_notes https://notes.andymatuschak.org/About_these_notes That said, you can have somethi

He says it's a custom site: https://notes.andymatuschak.org/About_these_notes https://notes.andymatuschak.org/About_these_notes That said, you can have something identical to this with Obsidian with a few plug-ins and their hosting service. https://obsidian.md/ https://obsidian.md/ https://github.com/deathau/sliding-panes-obsidian https://github.com/deathau/sliding-panes-obsidian