I followed the instructions at Quarto.org, integrated with VS Code. So they are text documents stored locally. I didn't realize observable-cli was open source.

I find it can't do nested logic the way observablehq.com can though. For instance, I like having inputs embedded in paragraphs of text, which requires having logic mixed in with a markdown cell. There are certain things that I can do on the web that don't work locally.

There's also https://observablehq.com/@asg017/introducing-dataflow, which I haven't tried yet.