In https://observablehq.com/ https://observablehq.com/ the platform itself is not open source but the core code that evaluates notebooks is open source, the var

In https://observablehq.com/ https://observablehq.com/ the platform itself is not open source but the core code that evaluates notebooks is open source, the various libraries used by notebooks are typically open source, and the content of those notebooks is all publicly visible (with license determined by each author). Aside: Personally I have found that the spreadsheet-like Observable model of tracking a dependency graph between cells and re-rendering dependents whenever a cell changes is much more pleasant than the Mathematica/Jupyter/etc. model where evaluation of cells initially happens from top to bottom at load time and then is afterward haphazard depending on the deliberate action of the viewer (which means it can easily get into inconsistent states). The resulting notebooks are (at their best) also IMO substantially better as written documents for readers, based on better text layout and richer tools for creating diagrams. Being JavaScript that runs in the viewer’s browser makes it much easier to build compute-heavy notebooks that rely on reader interaction, and easier for readers to participate as equals with authors.