uts, the Useless Toy Scheme is a Scheme bytecode interpreter. It’s almost fully R4RS-compliant but otherwise minimal. It needs the Boehm garbage collector to run. In an earlier incarnation this was known as Plonk; there is an all-Scheme version, and a Java implementation of the bytecode interpreter part. It’s known to not work right with JDK 1.1, and it will not be developed any further.