My rarest systems would include (all CIB):
Funtech Super A'Can
Pioneer LaserActive
Pippin @World
Casio PV-1000
Gakken TV Boy
Tomy Pyuuta
Epoch Cassette Vision series
et al.
Being an avid video game console collector, I have most of the systems mentioned and applaud those that have those really rare sysrems (and those trying to aquire them). I would have to say though my rarest system is the Panasonic FZ-35S (3DO 2, sometimes referred to the Panasonic M2) that was not released to the public, only commercially on a very limited basis. There were two models manufactured overall, but this 3DO 2 model was scrapped before it went public to the gaming community.
Terry
My collection --> Marriott_Guy's HUGE Video Game Console Collection - 95+ Systems!!