One of my first jobs had a legacy application that was based on Clipper. I never had to work with it directly (since I worked on the SQL successor) but reading the source code was still fascinating.
Fish is really great for an interactive shell, I love using it. Not so great when it comes to scripting though. For example I think there's still no way to easily exit a script on error except to manually check exit codes.
However I haven't tried writing scripts in zsh yet, just sh/bash.
Semi off-topic: The wikipedia article on Ed Esber is in dire need of a clean up https://en.wikipedia.org/wiki/Ed_Esber