Dr. Mario is a spin-off franchise of the Mario franchise. The series stars Dr. Mario, one of Mario's alter egos. Occasionally, the series has a Nurse Toadstool. The gameplay is similar to that of Tetris, except with pills being stacked in color coded order (each to eliminate a certain color virus).
Dr. Mario, the first game in the franchise, was released for the NES in 1990. It introduced the series' gameplay. Pills fall onto the playing screen (of colors red, blue, or yellow), and when four of one color are lined up, it deletes those four. After erasing all of a certain color, that corresponding virus disappears. After all viruses have been eradicated, the next level begins. Dr. Mario was also released on the Game Boy, as a grayscale edition.
Dr. Mario 64
Dr. Mario 64 was released on the Nintendo 64 in 2001. It maintained the same Dr. Mario gameplay, with the only real new update being a large graphical face lift. Dr. Mario 64 also had a Story mode, in which Wario is introduced. Dr. Mario and Wario fight against computer controlled opponents to retrieve stolen Megavitamins.
Tetris & Dr. Mario
Tetris & Dr. Mario was released on the Super Nintendo in 1994. It contains a graphically updated version of Dr. Mario, as well as a graphically updated version of Tetris. Other than those differences, the games were no different from their original NES versions.
Nintendo Puzzle Collection
Nintendo Puzzle Collection was a Japanese-only release for the Nintendo GameCube in 2003. The game was a compilation, featuring Panel de Pon (Tetris Attack), Dr. Mario, and Yoshi no Cookie (Yoshi's Cookie). All of the games had updated graphics and sound. Dr. Mario also featured many of the updates it had from Dr. Mario 64.
Dr. Mario & Puzzle League
Dr. Mario & Puzzle League is a Game Boy Advance game released in 2005. The version Dr. Mario in this game was similar to Dr. Mario 64 graphically and gameplay-wise. The game also included Puzzle League, which is in fact Tetris Attack (although the title 'Puzzle League' probably comes from Pokémon Puzzle League, which is another version of Tetris Attack).
Dr. Mario Online Rx
Dr. Mario Online Rx is a WiiWare game released in 2008. The game has all of the traditional gameplay aspects of the Dr. Mario franchise. Dr. Mario Online Rx also includes the ability to play as a Mii, rather than Dr. Mario. The game also has an online multiplayer mode via Nintendo Wi-Fi Connection, a series first. Dr. Mario Online Rx also included a Virus Buster minigame originally from Brain Age 2: More Training in Minutes a Day.
Chotto Dr. Mario
Chotto Dr. Mario is a DSiWare game released in 2008 (in Japan). The game design is very similar to that of Dr. Mario Online Rx, however Chotto Dr. Mario does not have the Virus Buster minigame. The game is also only for one player, rather than the multiplayer mode that was in Dr. Mario Online Rx.