The xs shell is a modified version of the es shell, in turn based upon the rc shell.

Interesting features include functional programming tools like lambdas and closures, exceptions, glob-style string matching (like simple regexps), and non-linear redirects (like a more flexible alternative to pipes).

Xs has a notably different syntax from bourne-derived shells, especially in control structures (braces replace do-end in while, for example).

The code should not be too hard to hack on, especially considering that part of the shell is written in xs. This also allows effective customization/modification to the shell in one's init file.

Compared to es, xs has some bugfixes, code cleanup, better readline integration, and syntax improvements.