To play the 400 in 1 NES ROM, you'll need an NES emulator. Here are some popular options:
If you're still interested in downloading a 400 in 1 NES ROM, here are some tips to help you do so safely: 400 in1 nes rom download link
While the specific list can vary slightly depending on the version of the pack, most 400-in-1 collections include a mix of legendary hits and obscure gems: To play the 400 in 1 NES ROM, you'll need an NES emulator