sodapopcan parent
It's not that unique. The one enterprise app I worked on (that was started with Rails 1) had all of: Prototype, jQuery, Backbone, Angular, React, Handlebars AND mustache, vanilla CSS, SASS, CSS in JS (or whatever it's called). I wouldn't be surprised if they've introduced Tailwind at this point.
This is also a project started w/ Rails 1, so I feel our experiences may be similar.
To be fair to both code bases - it's very impressive that they're still running, right?
Definitely!
It actually wasn't even THAT bad considering how huge it is. People still complained (admittedly myself included), but it had been TDD'd from the start so had very good test coverage, at least. Also, some people who had worked on really massive Java applications called it "really good!" so it's all about perspective, I suppose :)