Back in the '90s Bits Studios was working on a Die Hard game for the N64. Not following any of the films in particular, it would have seen you fighting through hospitals, a prison riot, and the streets of LA to stop an armed group from completing whatever grand plan they have for the city.
Although the studio got Die Hard 64 to a playable state, it was never shown. There were rumours the game was in development, but the recently uncovered cartridge shows the game was further along than you might expect considering how little was known about it.
According to Retro Collect, a forum member on Assembler Games revealed that they had a copy of the in-development game and found it to be playable but far from complete, sharing some screenshots of the game in action.
"The game is far from complete, and is split into three roms," the forum user told Retro Collect. "Each ROM has got about eight levels and around three of them are playable in each ROM (the rest are test levels, or unfinished levels with no enemies at all). [...] The maps are quite big, and fairly impressive for the Nintendo 64; for instance in the LA street level you have a few streets and you can go inside some buildings, but you don't have any pedestrians or cars running in the street."
Apparently, the game only has two lines of dialogue: "Yippee ki-yay" and "That must hurt." After a little while with the game I imagine Bruce will be getting a little dull if that's all he says.
The team never completed Die Hard 64, which was due out late in the console's life cycle. Though they went on to make Die Hard: Vendetta for the GameCube, Xbox, and PS2.