The Oberheim OB-8 is a polyphonic analogue synthesizer used by Prince. He used one on Purple Rain and it was the last Oberheim that he used. It remained in Prince's collection and was bought out whenever he wanted an analogue synth sound. It appears on later records like Newpower Soul and Rave Un2 The Joy Fantastic. The OB-8 was never used live by any of Prince's keyboard players.
Occasionally he'll bring in one of the old Oberheims, but very rarely. I think we only have the OB-8 left over now; the rest of the stuff has been sold off.