PhantomJS
We use CasperJS because we adopted it back in 2013 for JavaScript frontend testing. It was a really nice system back then compared to what else was out there; you had PhantomJS as a programmable browser that actually rendered CSS and everything, it was really fast (speed is a big downside of e.g. Selenium), and it was possible to make non-flaky frontend integration tests with it.
I wouldn't recommend it today, because PhantomJS is a basically dead project, and as a result, so is CasperJS. I expect we'll migrate to something else. We haven't in large part because 95% of our new tests are written with a simple Node.js-based unit testing framework we use that run 35K lines of unit tests covering most of our JS codebase in 3.6 seconds. And for the things where we want an integration test, CasperJS does work, and I think there's a good chance that waiting another year or two will result in our being able to switch to a much better option than what we'd get if we migrated now.
