From Wikipedia (abridged)
Resident Evil Zero, known in Japan as Biohazard 0 (バイオハザード0), is a survival horror game that was developed and published by Capcom for the Nintendo GameCube and released in 2002. It was the last of the main titles to use the original Resident Evil game system prior to the change in system ushered in by the release of Resident Evil 4.
The game's storyline serves as a prequel to Resident Evil, covering Rebecca Chambers' ordeal a day prior. The game was released on November 10, 2002 in North America, November 21, 2002 in Japan, February 28, 2003 in Australia and March 7, 2003 in Europe.
The main gameplay feature of Resident Evil Zero, dubbed the "partner zapping" system, is unique in the series in that instead of choosing a single character to play through the whole game, the player controls both the main characters, Rebecca Chambers, STARS Bravo team's medic, from Resident Evil and Billy Coen, an escaped ex-military convict, through the entire game. Both characters can travel together, with one character being controlled by the player and other by the computer, or split up and search separate areas each at the same time. This dual control is central to solving some of the puzzles in the game. The difference between the characters is that Rebecca can acquire chemicals with her mixing kit and can get into tight spaces, but has less health. In contrast, Billy can handle heavy objects, has a lighter and can sustain more damage than Rebecca, but cannot mix herbs.
The game also does away with the use of boxes placed in fixed locations for the player to store items in. Instead, the player can now drop items on the floor to make room for new ones, which they can later retrieve for future use. The locations of dropped items are displayed on the player's map.
A Wii version of Resident Evil Zero was released in Japan on July 10, 2008 as "Resident Evil Archives: Resident Evil 0". The Wii version is a direct port of the original GameCube game with added support for the Wii Remote and Nunchuk (without pointer controls) and the Classic Controller in addition to the GameCube Controller. It was also released in North America on December 1, 2009. IGN gave the Wii version a "poor" 4.5/10 while IGN Australia gave it a "mediocre" 5.4