Ikarus Scheme was announced on the comp.lang.scheme newsgroup. It's an open source R6RS Scheme system which does incremental native code compilation.
Ikarus is an optimizing compiler, so your Scheme code will run fast without the need to port hot spots to C "for performance". With an incremental compiler, you don't need a separate compilation step to make your program run fast. The best part is that the compiler itself is fast, capable of compiling thousands of lines of code per second.
More details at the Ikarus Scheme website.