Digimon:

The franchise was first created in 1997 as a series of virtual pets, akin to—and influenced in style by—the contemporary Tamagotchi or nano Giga Pet toys. The creatures were first designed to look cute and iconic even on the devices' small screens; later developments had them created with a harder-edged style influenced by American comics. The franchise gained momentum with its first anime incarnation, Digimon Adventure, and an early video game, Digimon World, both released in 1999. Several seasons of the anime and films based on them have aired, and the video game series has expanded into genres such as role-playing, racing, fighting, and MMORPGs. Other media forms have also been released.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Name the Digimon video game that was released in 1999.
Digimon World