Scheme

Standards

R7RS-small archive

R6RS

R5RS

Books

The Scheme Programming Language, 4th Edition

Teach Yourself Scheme in Fixnum Days

Implementations

Chez Scheme

Gerbil Scheme

CHICKEN Scheme

GNU Guile

MIT/GNU Scheme - GNU Project - Free Software Foundation

Toy implementations

(How to Write a (Lisp) Interpreter (in Python))