These pages detail various differences between Scheme implementations.
List of implementations tested:
BDC, Bigloo, Chez, Vicare, Chibi, Chicken v4, Chicken v5, Cyclone, Dfsch, Elk, FemtoLisp, Foment, Gambit, Gauche, Guile, Inlab, IronScheme, JScheme, Kawa, KSi, Larceny, LIPS, Llava, LMU Scheme, Mini-Scheme, MIT, Mosh, NexJ, Oaklisp, Owl Lisp, Picrin, Racket, Rep, RScheme, S7, Sagittarius, Scheme 9, Scheme48 and scsh, Schemik, SCM, Shoe, SigScheme, SIOD, SISC, Sizzle, STklos, SXM, TinyScheme, UMB, Unlikely Scheme, unsyntax, XLisp, Ypsilon.
Not all of these surveys have information on all these Schemes.
We have not managed to build and run VX, Spark, KSM, Luna, MScheme, QScheme, Rhizome/pi, and VSCM. For these and many other Schemes see the fairly complete list of Scheme implementations.