I've updated my space invaders emulator written in Factor to work with the new Factor GUI system. This means that Space Invaders can run in a seperate window from the main Factor GUI and you can even run multiple instances at a time.
While the emulator is running you can still use the Factor GUI to browse, run code, etc. You could even browse the 8080 CPU emulator data structures and memory while it is running.
A screenshot of two running space invaders instances is here.
As the emulator is a Factor gadget, hopefully it will run unchanged on Mac OS X and Windows. The updated emulator will be available in the upcoming Factor 0.81 or you get can get it from my darcs repository at: http://www.bluishcoder.co.nz/repos/factor