Well, "ridiculous_fish", the guy who sort of revived the fish shell is an engineer on the AppKit team at Apple: http://ridiculousfish.com

I remember installing and using fish 4 or 5 years ago; it was not a great experience -- but after he "took over", I switched and couldn't be happier with fish.

Interesting! My impression was that Apple engineers were prohibited from building anything outside of work.

According to Wikipedia[0], fish was originally created by Axel Liljencrantz in 2005. The commit history from GitHub does go back that far (I imagine it was imported somehow), so I assume it's complete. The first commit from ridiculous_fish is in 2011.

So if there is such a policy at Apple, I would expect that it doesn't prohibit contributing to already-public projects.

[0] http://en.wikipedia.org/wiki/Friendly_interactive_shell

That makes sense, the create of fish works at Apple: http://ridiculousfish.com/blog/about.html