Chez Scheme has always been an excellent Scheme implementation. It produces very fast object code and is a complete R6RS implementation with extensions. Chez Scheme was written by Kent Dybvig, who also wrote the excellent The SCHEME Programming Language (also available online).
The problem has been that Chez was a proprietary, closed system. Now Chez has been opened sourced. If you are a Schemer, you may want to take a look. I haven’t built it yet so I don’t have a take on how hard that is, but these directions make it look pretty simple: perhaps as simple as a configure and make install.
If you’re interested in learning Scheme, Dybvig’s book and Chez Scheme are an excellent way. And now you can get both at no cost. The CONTRIBUTING and CHARTER files indicate that Chez Scheme is an ongoing project that welcomes new developers. The open sourcing of it is really good news for the Scheme community.