There was another Perfect Dark game in development at one point, a follow-up to Xbox 360 launch game Perfect Dark Zero that would have been a "more realistic," seemingly grittier version of Rare's first-person shooter.
Unseen 64 offers our first look at Perfect Dark Core, a prototype project that never really seemed to take off at Goldeneye and Banjo Kazooie developer Rare. This Perfect Dark would have featured extended melee attacks and a grimier looking Joanna Dark. At some point in development, according to Unseen 64, Joanna was dropped in favor of a male lead. The game then evolved into some sort of proposed mech-based shooter.
Then it appeared to completely fizzle, with Rare changing direction.
Concept art and early animation of Perfect Dark Core and its spin-offs are available at Unseen 64, should you have a keen interest in looking at the remains of this game.