From the web page:

Cyclone is a brand-new Scheme-to-C compiler that allows practical application development using R7RS Scheme. Cheney on the MTA is used by Cyclone's runtime to implement full tail recursion, continuations, and generational garbage collection. In addition, the Cheney on the MTA concept has been extended to allow execution of multiple native threads. An on-the-fly garbage collector is used to manage the second-generation heap and perform major collections without "stopping the world".
Cyclone is the first compiler written entirely in the latest R7RS Scheme language standard, and the intent is to support as much of that language as possible.

Features include:

Support for the majority of the Scheme language as specified by R7RS.
New features from R7RS including libraries, exceptions, and record types.
Built-in support for Unicode strings and characters.
Hygienic macros based on `syntax-rules`
Low-level explicit renaming macros
Guaranteed tail call optimizations
Native multithreading support
A foreign function interface that allows easy integration with C
A concurrent, generational garbage collector based on Cheney on the MTA
Includes an optimizing Scheme-to-C compiler,
... as well as an interpreter for debugging
Support for many popular SRFI's
Online user manual and API documentation

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