This moved to category-implementations.
Scheme Implementation Chart
Here is a quick-and-dirty list of Scheme implementations.
Compiles Scheme to C and JVM.
A Scheme->C compiler with a good FFI.
Another Schme->C compiler. Version 4.0 will be out Real Soon Now ;)
This wiki runs on it. A scripting language scheme interpreter with good Unicode support.
R4RS Scheme, but for Palm Os
Runs on the JVM
A good scheme for people who want to learn scheme. It also has an IDE, and a GUI toolkit. Includes MzScheme, DrScheme, and MrEd. Some people also like PLT for production use and as a research platform.
The primary design goal was clarity and good design.
The SCheme SHell, based on Scheme48. This adds a lot of very interesting facilities for POSIX system interfacing.
A Scheme interpreter in Java, making the whole Java library available to Scheme, and still being very fast (for an interpreter)
Scheme to C compiler