Monar is a free interpreter for R6RS Scheme.
Currently it covers a little of R6RS core scheme, utf-8 I/O, quasiquote, apply , regexp , traditional macro, 30bit fixnum , simple port , simple CGI and format.
And Wiki works on Monar@FreeBSD+Apache.
http://monar.monaos.org/wiki/LambdaWiki
Downloads and More Information
Source code and Monar documentation can be found on the web at:
(via comp.lang.scheme)