People might not know that, since it’s mostly in French, but France has somthing similar as open source for their tax system: https://github.com/openfisca/openfisca-france/
Nice, the french also are at the frontier of law-computing i'd say see Catala Lang [1] 1. https://catala-lang.org/
Have wondered whether attorneys would find it easier to work in a programming language than english, once they'd learned the former? Do any have strong opinions on this?