This is Debian's prepackaged version of es.  Es is an extensible shell.

The language was derived from the Plan 9 shell, rc, and was influenced
by functional programming languages, such as Scheme, and the Tcl
embeddable programming language.

The package was previously maintained by Joost Witteveen, James Troup
and Raul Miller.  The current package was put together by Gergely
Nagy.

Upstream sources from Paul Haahr and Byron Raitzis are available from:
	ftp://ftp.sys.utoronto.ca/pub/es/es-0.9-beta1.tar.gz

es was written by Paul Haahr and Byron Rakitzis and is in the public
domain.

es is under the following copyright:

     We hold no copyrights or patents on the source code, and do not
     place any restrictions on its distribution.  We would appreciate
     it if any distributions do credit the authors.