Chez scheme was recently released as free software. Not sure how it compares to SBCL, but it blows all the other scheme implementations out of the water: <a href="https:&#x2F;&#x2F;www.nexoid.at&#x2F;tmp&#x2F;scheme-benchmark-r7rs.html" rel="nofollow">https:&#x2F;&#x2F;www.nexoid.at&#x2F;tmp&#x2F;scheme-benchmark-r7rs.html</a><p><a href="https:&#x2F;&#x2F;github.com&#x2F;cisco&#x2F;ChezScheme" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;cisco&#x2F;ChezScheme</a>