See https://r7rs.org/, https://get.scheme.org/, https://www.r6rs.org/implementations.html.
Compiles to C, JVM and .NET.
A very fast cross-platform native code compiler and a smaller but compatible interpreter.
A very small library intended for use as an extension and scripting language in C programs.
Compiles to C. Good FFI? and large ecosystem.
Compiles to C. Allows practical application development using R7RS Scheme. Focuses on concurrency.
This wiki runs on it. A scripting language scheme interpreter with good Unicode support.
The GNU Scheme interpreter, designed to have good integration with C programs. A nice extension language.
Dialect based upon Gambit.
R6RS Scheme for the .NET Framework.
Runs on the JVM.
A dialect of Scheme. Supports many standards. Built on top of Chez.
Small and portable R5RS implementation. Tightly integrated with SLIB, by the same author.
Mostly compliant with R7RS. Includes an object system based on CLOS, GTK+ bindings, POSIX threads, and other useful facilities.
This is not to say these implementations are incomplete/unusable/abandoned. Some are very much complete and can be used or studied.
The SCheme SHell, based on Scheme48. This adds a lot of very interesting facilities for POSIX system interfacing.
The primary design goal was clarity and good design.
A Scheme based extension language kit.
Is a simple and efficient runtime for many standards.
R4RS Scheme, but for Palm Os. Final version from 2008.
Very much dead. Seemingly never released.
Compiles to C. Last release in 2016.
Could anyone check on these?
R6RS Scheme incremental compiler to i32 and i64 native code.
A variant of Scheme48 for distributed computation.
An R5RS Scheme interpreter in OCaml.
A purely functional dialect of R7RS Scheme. Small, embeddable, cross-platform. Has own FFI.
A scheme for WinCE based handhelds.
Compiles to C, has Dylan-like OO features.
A Scheme interpreter in Objective Caml.
A Scheme interpreter in Java, making the whole Java library available to Scheme, and still being very fast (for an interpreter)
The framework for creating web applications using the SISC interpreter.
Is the name for an implementation and dialect of scheme
A lightweight Scheme interpreter
An embeddable C++ implementation