Internet Arcade
archive.org/details/internetarcade
The Internet Archive's collection of over 900 classic arcade games playable directly in the browser — including Pac-Man, Donkey Kong, Centipede, Space Invaders, and hundreds of more obscure titles.
Why it is useful
The most complete preservation of arcade gaming history available to the public. Playing these games in context — not as remakes or emulator downloads, but the original ROM running in the browser — is a different experience from watching gameplay videos. The obscure titles are as interesting as the famous ones: seeing what didn't survive shows as much about the era as what did.