Just now there are 74 implementations of Scheme listed <a href=http://community.schemewiki.org/?scheme-faq-standards#implementations>here</a>.
I fantasize trying some of them and reporting here on which ones run most of my code.
Today is 2013 July 21.
<dl>
<dt><a href=http://dynamo.iro.umontreal.ca/wiki/index.php/Main_Page>Gambit</a>
<dd>It passes all but items 4 and 6 of <a href=../../code/Scheme/qualifications.html>these requirements</a>.
That’s good enough for now.
<p>Performance: the routine:
<pre>(let lc ((n 1000000)(s 0)) (if (= n 0) s
  (lc (- n 1)(+ s (- n)))))</pre>
plus launching and quitting the REPL took .3 sec on MzScheme and 14.6 on Gambit.
<p>“((fileVal "Farey") 1024)” takes 10 sec on MzScheme version 352 but had not finished after a minute on Gambit 4.6.8.
<p>I tried out most of my repository code and it performed all of them.
I found two constructs that I use that are not required in R5RS.
I easily fixed them.
<dt><a href=http://practical-scheme.net/gauche/index.html>Gauche</a>
<dd><a href=http://practical-scheme.net/gauche/man/gauche-refe.html>Manual</a>,
<a href=http://practical-scheme.net/gauche/man/gauche-refe_5.html#Standard-conformance>conformance</a>
<br>I did ./configure and make.
“make test” passed.
“make install” needs root access which I am unwilling to grant.
The interactive shell is called “gosh” but I can't find it.
So much for Gauche.
<dt><a href=http://hscheme.sourceforge.net/>HScheme</a>
<dd>Scheme written in Haskell!
I will not try this for now but it is well worth reading the comments at the link.
<dt><a href=http://llava.org/>Llava</a>
<dd>A peculiar Scheme wrapper for Java.
</dl>