Which Nintendo console was codenamed “Dolphin” during development?

The Nintendo GameCube was codenamed “Dolphin” during development.

Nintendo revealed the Dolphin project in 1999 as the successor to the Nintendo 64. The final console name, GameCube, emphasized its compact cube-shaped design and its use of small optical discs rather than cartridges.

The Dolphin name is sometimes confused with Nintendo’s later Wii development codename, Revolution. Dolphin also became the name of a popular open-source emulator for GameCube and Wii games, because the emulator adopted the original hardware codename.

GameCube launched in Japan in September 2001, followed by North America and Europe later that year. Its notable games included Super Smash Bros. Melee, Super Mario Sunshine, The Legend of Zelda: The Wind Waker, and Metroid Prime. The console sold more than 21 million units worldwide, placing it below the Nintendo 64 in lifetime hardware sales.