3DScheme
   Two systems for Windows with built in "industrial-strength" solid modeler based on the ACIS solid modeler Geometric Modeling Kernel.
   http://www.schemers.com/3dscm1.html

An Executable Denotational Semantics for Scheme
   SchemeDS, as defined in R5RS. Program coded in R5RS Scheme. Description, documents, downloads. [AppSolutions Software Licensing]
   http://www.appsolutions.com/SchemeDS/

Better Scheme
   Language designed and largely implemented, now a matter of coding, documenting. Goals: high consistency; improve language's functional nature; consistency with lambda calculus; optimize, but not at cost of other goals.
   http://www.cs.oberlin.edu/~jwalker/bscheme/

Bigloo
   System with one goal: enable Scheme programming style where C(++) is usually needed; makes Scheme practical via features found in most normal languages but not Scheme and functional programming. Generators for C code, Java Virtual Machine, .NET bytecode.
   http://www-sop.inria.fr/mimosa/fp/Bigloo/

CMU AI Repository Free/Shareware Scheme Implementations
   Yet more Scheme implementations from the CMU AI Repository. Many of these are also available from the Indiana University Scheme Repository.
   http://www.cs.cmu.edu/afs/cs/project/ai-repository/ai/lang/scheme/impl/0.html

Chez Scheme
   Reliable, high performance implementation, by Cadence Research Systems. Free version exists. [Commercial]
   http://www.scheme.com/

Chicken
   A Scheme compiler which compiles a subset of R5RS into C. Uses the ideas presented in Baker's paper "Cheney on the MTA". It is highly portable, reasonably efficient and makes interfacing to C and C++ very easy.
   http://www.call-with-current-continuation.org

DrScheme
   Full Scheme programming environment for Macintosh, many Unixes, Windows. Has module and object systems, platform-independent graphics. Ideal for beginners; one of the major design goals is a flexible teaching environment.
   http://www.drscheme.org/

EdScheme
   Interpreter for Macintosh or Windows. Has "friendly and convenient interactive programming environment" with language sensitive editor, full documentation. [commercial, free 14 day download]
   http://www.schemers.com/edschem.html

Elk Scheme: The Extension Language Kit
   New site. Embeddable, reusable extension language subsystem for programs coded in C/C++, also a useful standalone Scheme implementation with interfaces to POSIX, Unix, X11.
   http://sam.zoy.org/elk/

Elk: Scheme-based Extension Language Kit
   Old site, last update 1997. Embeddable, reusable extension language subsystem for applications written in C/C++, also a useful standalone Scheme implementation with interfaces to POSIX, Unix, X11.
   http://www-rn.informatik.uni-bremen.de/software/elk/

EuScheme Sources
   Small implementation of Level 0 EuLisp, downloads in formats: tar, tgz, zip.
   http://people.bath.ac.uk/masrjb/Sources/

Galapagos
   An interactive multithreaded Scheme interpreter with turtle graphics for Windows 95, based on SCM.
   http://www.cs.bgu.ac.il/~elad/GALAPAGOS/

Gambit
   A portable, high-performance implementation of Scheme based on an optimizing compiler by Marc Feeley. Developed at University of Montreal.
   http://www.iro.umontreal.ca/~gambit/

Gauche
   An R5RS Scheme implementation developed to be a handy script interpreter. Quick startup, built-in system interface, native multilingual support. [Open source, BSD license]
   http://www.shiro.dreamhost.com/scheme/gauche/

Indiana University Scheme Repository: Implementations
   Even more Scheme implementations freely available from the Indiana U. repository.
   http://www.cs.indiana.edu/scheme-repository/imp.html

Infer Project
   Statically-typed Scheme dialect, written in Infer, combines many of the best features of Scheme and ML. NSF funded.
   http://www.cs.indiana.edu/~chaynes/infer.html

Inlab Scheme
   A commercial Scheme which is freely available for non-commercial use on Linux and FreeBSD. It has support for several features like bitmap/greymap processing and can be used as a general tool for image processing, OCR or specialized optical object and pa
   http://www.inlab.de/scheme/

KSM-Scheme
   A R5RS Scheme interpreter which integrates with C, allowing calling of C functions and accessing C variables from Scheme. It provides a mechanism to load C shared libraries. It runs on x86 and PowerPC based Linux systems.
   http://square.umin.ac.jp/~hchang/ksm/

Kali Scheme
   A distributed implementation of Scheme that permits efficient transmission of higher-order objects such as closures and continuations.
   http://community.schemewiki.org/kali-scheme/

LEGOScheme
   Lego/Scheme compiler for Lego MindStorms Robot kits, alternative to Visual Basic. Description, documents, downloads.
   http://www.indiana.edu/~legobots/legoscheme/

Larceny Project
   Simple, efficient Scheme run-time system, for SPARC architecture. Petit Larceny is portable and emits C, for Linux (Intel IA32), Macintosh OS X (PowerPC), Solaris (SPARC), Windows. Common Larceny runs on Microsoft Common Language Runtime (CLR), emits MS
   http://www.ccs.neu.edu/home/will/Larceny/

LispMe
   Newer versions here. Scheme system for the Palm Pilot PDA developed by Fred Bayer.
   http://www.lispme.de/lispme/index.html

MIT Scheme
   From MIT, for many systems, has comprehensive code library, includes most functionality of ANSI Standard Common Lisp (CLtL2), many low-level OS interactions. Distributed with system is LIAR (LIAR Imitates Apply Recursively), optimizing compiler that outpu
   http://www.swiss.ai.mit.edu/projects/scheme/

MzScheme
   Small, embeddable, scripting PLT Scheme implementation: R5RS compliant, full numerical tower, threads (all platforms), exceptions, modules, class-based objects, regular-expression matching, TCP/IP. For Macintosh, Unix, Windows 32-bit.
   http://www.plt-scheme.org/software/mzscheme/

Narsi
   Portable scheme interpreter by Britt Park. Other free software: Cdoc, simple program to generate pretty TeX output from annotated C/C++ code. Userblock, simple user space block device driver kit for Linux. UVFS, user space filesystem kit.
   http://www.sciencething.org/geekthings/

Oaklisp
   Object-oriented Scheme dialect with first-class types, multiple inheritance, lexically distributed method definitions. based on bytecode emulator, yet reasonably fast. Description, downloads, bibliography. [Open Source, GPL]
   http://www.bcl.hamilton.ie/~bap/oaklisp/

PC Scheme
   Texas Instruments system for DOS OS; no longer maintained; download formats: source, executable/binary.
   ftp://swiss-ftp.ai.mit.edu/pub/pc-scheme/

PLT Scheme
   Advocacy and authoring group, umbrella name for family of implementations: DrScheme (Scheme, MzScheme, MrEd); books: How to Design Programs, How to Use Scheme; and TeachScheme! project. University-based, supported by many volunteers writing code, document
   http://www.plt-scheme.org/

Petite Chez Scheme
   A complete Scheme system that is fully compatible with Chez Scheme but uses high-speed threaded interpreter technology in place of Chez Scheme's incremental native-code compiler. [Freeware]
   http://www.scheme.com/petitechezscheme.html

Pico
   Tiny, expressive; made to teach advanced computer science ideas to non-computer science students; mixes power of languages like Scheme, with standard infix notation known from calculus. Has: garbage collected tables (arrays), higher order functions, objec
   http://pico.vub.ac.be/

Pocket Scheme
   For MIPS, SH3, ARM-based Windows CE devices. Supports Aubrey Jaffer's SLIB, has initialization file for same, parenthesis-balancing text editor. Windows NT version exists. [Open Source, Artistic License]
   http://www.mazama.net/scheme/pscheme.htm

Pseudoscheme
   Embeds Scheme in Common Lisp.
   http://mumble.net/~jar/pseudoscheme/

QScheme
   A fast, small Scheme interpreter which is mostly compliant with the R5RS standard.
   http://www.sof.ch/dan/qscheme/index-e.html

RScheme
   Portable, extended Scheme with reflective object(-oriented) system, operating system services, modules, threads, many system programming features (integrates with, compiles to C or bytecodes) and useful extensions. [Open Source]
   http://www.rscheme.org/

SCM
   A portable Scheme implementation written by Aubrey Jaffer.
   http://www-swiss.ai.mit.edu/~jaffer/SCM.html

SIOD: Scheme in One Defun
   Very small, portable implementation, has some database, Unix programming, CGI scripting extensions. Runs on DOS, Linux, Unix, Windows. Free source downloads.
   http://people.delphiforums.com/gjc/siod.html

STk
   R4RS Scheme interpreter with interface to access Tk graphical package; can be seen as a standard Tk package with Tcl replaced by a Scheme interpreter. Has efficient CLOS-like object-oriented system, STklos.
   http://kaolin.unice.fr/STk/

STklos
   Derived from STkn implementation based on an ad-hoc virtual machine, byte compiler; compilable as library to embed in other programs, has object system with MOP, multiple inheritance, generic functions, multimethods, module system, full R5RS tower of numb
   http://www.stklos.org/

SXM, CXEMA
   Portable Scheme implementation, conforms to IEEE/ANSI standard, supports all features of R5RS Report, many features of Chez Scheme and various SRFIs. Derived from XScheme: object system dropped, many changes, additions.
   http://www.malgil.com/sxm/

Scheme 48
   Jonathan A. Rees's unofficial page: history, links, status.
   http://mumble.net/~jar/s48/

Scheme 48 User's Guide
   HTMLized by Margaret Fleck, one of the authors of Envision.
   http://www.cs.hmc.edu/~fleck/envision/scheme48/user-guide.html

Scheme Implementations and Mailing Lists
   A list of Scheme implementations from the Scheme FAQ maintained by Mark Kantrowitz.
   ftp://ftp.cs.indiana.edu/pub/scheme-repository/doc/misc/scheme_2.faq

Schoca (Scheme for OCaml)
   An implementation of the Scheme language in OCaml. The primary purpose of Schoca is the use as an embedded extension language in OCaml applications. [Open source, GPL]
   http://sf.net/projects/chesslib

Scsh
   Scheme Shell, broad-spectrum system programming environment for Unix, embedded in R5RS Scheme 48. Supports concurrent system programming, sophisticated I/O and automatic garbage collection for process resources.
   http://www.scsh.net/

Scsh FAQ
   The FAQ for Scsh, the Scheme Shell.
   http://www.alphanet.ch/~schinz/scsh-faq/scsh-faq_toc.html

Sizzle
   A Scheme interpreter implemented as a library which can be embedded into C programs, as well as a standalone interpreter. Mostly R5RS, Guile compatible, and includes regular expressions and most Posix functions.
   http://uebb.cs.tu-berlin.de/~magr/sizzle/sizzle.en.html

Sketchy
   Interpreter for pure functional applicative Scheme dialect, a variant of pure LISP plus global definitions (define), first-class continuations (call/cc), input/output functions (read, write, ...). Downloads: source, binaries. Sells: tutorial, reference ma
   http://www.t3x.org/sketchy/

Stalin
   A powerful optimizing Scheme compiler from Jeffery Mark Siskind at the NEC Research Institute. Sacrifices functions such as call/cc in favor of efficiency, but generated code is remarkably bulletproof and fast.
   http://www.cis.upenn.edu/~screamer-tools/home.html

T
   Scheme-like language developed at Yale; is to Scheme rather as NIL is to Lisp; mainly of interest to historians and theoreticians. FTP for v3.1.
   ftp://ftp.cs.indiana.edu/pub/scheme-repository/imp/t/

T History
   Fairly detailed, by Olin Shivers.
   http://www.paulgraham.com/thist.html

T Project
   History with: downloads, contributors, timeline, publications, influence, users, successors, Olin history errata. By Jonathan A. Rees.
   http://mumble.net/~jar/tproject/

T Revival Project
   Scheme dialect and implementation, incompatible with R5RS, but an R3RS compatibility layer exists; to grow more compatible with R5RS over time. Description, manual, downloads, mail list, IRC, contacts, plans.
   http://mumble.net/~campbell/t/t.html

The Ksi Scheme Interpreter
   Ksi is a portable, embeddable Scheme implementation written in C. Unfortunately its documentation is all in Russian at this point.
   http://ksi.sourceforge.net/

TinyScheme
   Based on Mini-Scheme, tiny implementation, almost a full R5RS Scheme. Goal: embedded scripting use, but works as standalone interpreter and extensible shell tool. Recent changes reduced executable size to about 64KB on Linux/x86. [BSD]
   http://tinyscheme.sourceforge.net/

Unlikely Scheme
   Small, standard-complying implementation, in C++. [Open source, zlib license]
   http://marijn.haverbeke.nl/unlikely/

VSCM
   A portable Scheme implementation written by Matthias Blume of Princeton University. No longer actively developed.
   http://www.cs.princeton.edu/~blume/vscm/

Vx-scheme
   A compact (<64 Kb) implementation of R4RS Scheme that compiles for VxWorks/Tornado (and is integrated with the system symbol table). [Open source, Artistic License]
   http://colin-smith.net/vx-scheme/

WinScm
   Scheme environment for Windows 3.1/95; interpreter independent, though defaults to Jaffer's SCM. Used at University of Lille 1, France, for introductory programming course. Free downloads. English, Française.
   http://www2.lifl.fr/~routier/enseignement/winscm/winscmeng.html

XLISP
   A superset of the Scheme dialect of Lisp with extensions to support object-oriented programming.
   http://www.mv.com/ipusers/xlisper/

XLisp-Plus
   Lisp version based on, and evolutionary improvement on, experimental XLisp.
   http://www.almy.us/xlisp.html

XLisp-Stat
   Based on XLisp, but with built-in statistics support.
   http://www.stat.uiowa.edu/~luke/xls/xlsinfo/node1.html