Interesting presentation on the thoughts behind Observable, how the reactivity is implemented in Javascript and what you can do with the notebooks:
https://www.youtube.com/watch?v=lNbqfQlGkzc▾
The notebook runtime code is also on Github. I’m thinking that might be interesting to do alternate UIs or frontends to the notebooks: graph-based for example, or then something that is not editable but for publishing only:
https://github.com/observablehq/runtime