From the homepage:

Ikarus Scheme is a free optimizing incremental native-code compiler for Scheme as specified in the Revised^6 Report on the Algorithmic Language Scheme.

 Ikarus Scheme is free to download, to distribute, to modify, and to redistribute. The complete source is available according to the GNU General Public License (GPL3).
 Ikarus Scheme is an optimizing compiler, so your Scheme code will run fast without the need to port hot spots to C "for performance". With an incremental compiler, you don't need a separate compilation step to make your program run fast. The best part is that the compiler itself is fast, capable of compiling thousands of lines of code per second.
 Finally, Ikarus Scheme is an R6RS compiler. R6RS is the latest revision of the Scheme standard. The current release of Ikarus supports over 90% of the most important features R6RS, and later releases will bring Ikarus closer to full R6RS conformance. R6RS libraries, scripts, record types, condition system, exception handling, unicode strings, bytevectors, hashtable, and enumerations are among the supported features.