Perfect Dark is a FPS developed by RARE Ware for the Nintendo 64 and released in 2000. Martin Hollis, the director of GoldenEye 007 and Perfect Dark, described the development of the game in an interview with Retro Gamer magazine. He explained that Rare rejected the prospect of working on the GoldenEye sequel Tomorrow Never Dies “without hesitation”, as the development team felt they had spent too much time immersed in the James Bond universe.
Originally Hollis hoped that the difference between light and dark would be a significant feature of the gameplay, and the title was intended to reflect this focus. A flashlight was implemented by Steve Ellis (responsible for much of the multiplayer mode in GoldenEye), but it was not included in the final game due to the limitations of the N64 hardware. [Info from Wikipedia]
In the images preserved in the gallery below, you can see many beta differences: different weapons, changes in the levels, characters unseen from some of the single player missions (the grey Aliens seem to have been used more in the beta and they were enemies, while in the final game the grey aliens are friends), the removed “Face Mapping” feature that let players to map their face on the game’s characters thanks to the gameboy camera (an option removed because of the Columbine High School massacre in 1999), censored red blood, removed multiplayer maps and much more.
We have a deeper article that compares most of the major beta differences, check the Perfect Dark Beta Analysis!