The previously commercial Scheme implementation (for more than 30 years) known as Chez Scheme from Cadence Research Systems (which was aquired by Cisco in 2012) was released as Open Source software using the Apache Licence 2.0.
This is a pretty cool move by R. Kent Dybvig and Cisco making this high quality implementation available to the general public. Chez has, among other things, support for compiling Scheme sources to native machine code. Something that my go-to Scheme GNU Guile doesn't feature (although there are long term plans into that direction, as far as I know).
In case you're interested: