Scheme 9 from Empty Space, Reimagined. S9fES is a mature, portable, and comprehensible interpreter for R4RS Scheme. The core interpreter is written in pure ANSI C (C89), so it runs on all platforms offering a C compiler. It can even be compiled natively on Plan 9. On Unix-based systems (or MinGW), it also offers an interface to common Unix system calls and Curses routines.