esh is a new shell for Unix, written completely from scratch. It is
very small, both in number of lines of source code and in memory
consumption. The whole shell is about 5000 lines of C source code, and
occupies about twice as little memory as bash in some cases.

However, esh is also extremely flexible, with a real programming
language at the core. The syntax is a simplified form of Scheme.  The
current version is 0.8, though it is already stable and
featureful. The reason for the low version number is lack of
real-world testing. It is released under the GPL, of course.

WWW: http://slon.ttk.ru/esh/