Scheme implementations are listed in the Scheme FAQ posting,
Free Scheme implementations include PC-Scheme, PCS/Geneva, MIT Scheme (aka
C-Scheme), SCM, Hobbit, Gambit, T, Oaklisp, Elk, Scheme->C, SIOD
(Scheme in One Defun), XScheme, Fools' Lisp, Scheme48, UMB Scheme,
VSCM, Pixie Scheme, HELP (a lazy Scheme), Similix, FDU Scheme,
PseudoScheme, Scheme84 and Scheme88.
Commercial Scheme implementations include Chez Scheme, MacScheme, and EdScheme.
Of the free Scheme implementations, the following are implemented in Lisp: 
 Peter Norvig's book "Paradigms of AI Programming" has a chapters about
 Scheme interpreters and compilers, both written in Common Lisp. The
 software from the book is available by anonymous ftp from
 ftp://mkp.com/Norvig/ and on disk in Macintosh or DOS format from
 the publisher, Morgan Kaufmann. For more information, contact: Morgan
 Kaufmann, Dept. P1, 2929 Campus Drive, Suite 260, San Mateo CA 94403,
 or call Toll free tel: (800) 745-7323; FAX: (415) 578-0672
 PseudoScheme is available free by anonymous ftp from
 swiss-ftp.ai.mit.edu:/archive/pseudo/pseudo-2-8.tar.Z [18.43.0.152]
 It is Scheme implemented on top of Common Lisp, and runs in Lucid,
 Symbolics CL, VAX Lisp under VMS, and Explorer CL. It should be easy
 to port to other Lisps. It was written by Jonathan Rees
 (jar@altdorf.ai.mit.edu, jar@cs.cornell.edu). Send mail to
 info-clscheme-request@mc.lcs.mit.edu to be put on a mailing list for
 announcements. Conforms to R3RS except for lacking a correct
 implementation of call/cc. It works by running the Scheme code through
 a preprocessor, which generates Common Lisp code.
 Scheme84 is in the public domain, and available by mail from Indiana
 University. It runs on the VAX in Franz Lisp under either VMS or BSD Unix.
 To receive a copy, send a tape and return postage to: Scheme84
 Distribution, Nancy Garrett, c/o Dan Friedman, Department of Computer
 Science, Indiana University, Bloomington, Indiana. Call 1-812-335-9770
 or send mail to nlg@indiana.edu for more information. It will also
 run in Jeff Dalton's port of Franz Lisp to Net/Free/386BSD on 386-like
 machines. (See the Lisp FAQ for information on Franz Lisp.)
 Scheme88 is a re-implementation of Scheme84 to run in Common Lisp. It
 available by anonymous ftp from
 ftp://rice.edu/public/
 and also from the Scheme Repository.