It's a minimal embeddable Scheme created by Bill Schottstaedt at CCRMA, the Stanford computer music centre. it's similar in scope to Guile or TinyScheme (from which it was originally forked), and is linguistically similar to Clojure and Janet in that it is fundamentally Scheme, but borrows heavily from Common Lisp (keywords, environments, CL macros). It's mostly used in computer music projects (Common Music, Snd, Radium, and others), but not only - there are some folks on the mailing list who use it as an embeddable DSL for "regular" engineering projects too. I built Scheme For Max on S7, and have been very happy with the choice for my constraints.
