Earlier quoted context omitted.
I am going to :+1: the UK census site - built on code developed by the gov.UK digital service, it has been apparently bulletproof at taking 20 million plus individual households through a moderately complex survey. sometimes it can be done right. And it uses a framework :-)
Which framework?
Edit: Just remembered it's all open source too! Look here and search for repos beginning "eq-". Survey runner is the app I believe. When I was there the plan was to use that, though perhaps they eventually wrote a fresh app. Anyway the code should all be there https://github.com/ONSdigital?q=Eq&type=&language=&sort=