S9fES is an interpreter for a broad subset of (R4RS) Scheme. It is
written in ANSI C (C89) and Scheme and it runs in many popular
environments, including *BSD, Linux, Plan 9, and the unmentionable
horror.

The S9fES code strives to be simple and comprehensible. It is
particularly interesting to people who want to try Scheme without
having to jump through too many hoops (S9fES is very portable) or
study the implementation of Scheme (in a language other than Scheme).

WWW: http://www.t3x.org/s9fes/