This is xs 1.3.1; see doc/CHANGES.
XS is the eXtensible Shell, a command line interpreter featuring Lisp-like semantics (lists, function parameters, closures, exceptions, lexical bindings, lambdas, etc.) and a conventional syntax.
The package includes extensive documentation. Sample scripts to define library functions, tools and utilities are found in https://github.com/FOSSUnleashed/XS-library.git .