Scheme 9 from Empty Space is an interpreter for a broad subset of R4RS Scheme, and runs in many popular environments, including Linux, *BSD, the unmentionable horror, and Plan 9. The S9fES code strives to be simple and comprehensible. It is particularly interesting to people who want to (a) try Scheme without having to jump through too many hoops (S9fES is very portable); or (b) study the implementation of Scheme (in a language other than Scheme). A free online textbook describing the system is also available.