Worth pointing out: France is not adopting existing open source software, they're building their own software and releasing it under the MIT licence. Most of it (or all of it?) is Django backend + React frontend (using a custom-built UI kit).

Home page for the entire suite (in French) with some screenshots: https://lasuite.numerique.gouv.fr/

Code bases are on GitHub and they use English there: https://github.com/suitenumerique/

Dev handbook (in English): https://suitenumerique.gitbook.io/handbook

Not French and I can't say I personally tried deploying any of them, but I've been admiring their efforts from afar for a while now.