What are some alternatives?
When comparing Rush and fish, you can also consider the following products
zsh - The Z shell (Zsh) is a Unix shell that can be used as an interactive login shell and as a powerful command interpreter for shell scripting.
DASH - DASH is a secure, blockchain-based global financial network which offers private transactions.
rc - a shell - This is a reimplementation for Unix, by Byron Rakitzis, of the Plan 9 shell.
GNU Bourne Again SHell - Bash is the shell, or command language interpreter, that will appear in the GNU operating system.
the xonsh shell - Xonsh is a Python-powered, cross-platform, Unix-gazing shell language and command prompt.
Bash - A simple and fast way to hangout with friends