(PSI) A portable scheme interpreter by Ozan Yigit firstname.lastname@example.org, David Keldsen and Pontus Hedman that includes a simple DAG compiler and a virtual machine. It can be used as an integrated extension interpreter in other systems and allows easy addition of new primitives. There are some unique debugging and tracing facilities. Acceptable performance results from a fairly straight-forward implementation. Continuations are fully and portably supported and perform well. PSI is based on the simple compilers and virtual machine in Kent Dbyvig's thesis.
The pre-release version conforms to R4RS with a number of useful extensions.