I believe that Kent Dybvig, author of The Scheme Programming Language, was one of the chief creators of ChezScheme. Over the years I heard good things about it, chiefly that it was very fast. Also the full version was expensive (~$1,000), although they did have a free interpreter (Petite ChezScheme). With the sale of it a few years ago, it seemed to disappear from view: E-mails to Cisco would not receive replies.
Seems to be quite good news that it is now open source. Wonder if arc would run under it and if it would be faster?