For detailed information about this series, see: Galapedia
Galaxian is a series of space shooter games created by Namco and part of the UGSF universe.
The released games are:
Galaxian (October 1979), Arcade. Later released for Apple II, Atari 400/800, Atari 2600, Atari 5200, Bally Astrocade (Galactic Invasion), Coleco VFD table top, ColecoVision, Commodore VIC-20, Commodore 64, MSX, NEC PC-8801, Sharp X1, ZX Spectrum, Famicom, Coleco Mini-Arcade and Wii Virtual Console.
Galaga (July 23, 1981), Arcade. Later released for Atari 7800, MSX, TRS-80 Color Computer, Famicom/NES, Wii Virtual Console and Xbox Live Arcade. The NES version was also enclosed in the NES Classic Edition.
Gaplus (April 1984), Arcade. Also known as Galaga 3, was later released on Mobile Phone.
Galaga '88 (1987), Arcade. Later released for X68000, for NEC PC Engine with the title Galaga '90 outside Japan, for Game Gear with the title Galaga '91 in Japan and Galaga 2 in Europe, and for Wii Virtual Console.
Galaxian 3 (1990), Arcade, also known as Galaxian³: Project Dragoon. Released for PlayStation in 1996, featuring an extra game called Galaxian³: The Rising of Gourb.
Attack of the Zolgear (1994), Arcade. Conversion of Galaxian 3, it is also known as Galaxian³: Attack of the Zolgear.
Galaga 3D Impact (June 23, 2011), Nintendo 3DS. Relesed within Pac-Man & Galaga Dimensions.
Galaga Assault (October 2015), Arcade. Including a new mode as well as an updated version of Galaga.
Galaga Arrangement (1995), Arcade. Released within Namco Classic Collection Vol. 1.
Galaga: Destination Earth (September 23, 2000), Windows, Game Boy Color, PlayStation.
Galaga X (2006), iOS.
Galaga Legions (August 20, 2008), Xbox Live Arcade, PlayStation 3 via PSN.
Galaga Remix (2009), iOS.
Galaga Special Edition (October 8, 2010), iOS.
Galaga Legions DX (June 29, 2011), Xbox Live Arcade, PlayStation 3 via PSN.
Space Galaga (January 24, 2014), Android, iOS. A Space Dandy-themed remake of Galaga.
Galaga: Tekken 20th Anniversary Edition (April 29, 2015), iOS, Android. A Tekken-themed remake of Galaga.
Galaga & Galaxian (September 9, 1995), Game Boy.
Galaga 30th Anniversary Collection (July 23, 2011), iOS. It includes Galaxian, Galaga, Gaplus and Galaga '88.
Pac-Man & Galaga Dimensions (June 23, 2011), Nintendo 3DS. Includes Pac-Man, Galaga, Pac-Man Championship Edition, Galaga Legions, and the new Pac-Man Tilt and Galaga 3D Impact. It also includes a trailer for the Pac-Man: The Adventure Begins TV series, titled Pac is Back.
Links to other series
Note: Galaxian 3 is the first game to mention the "UGSF" (United Galaxy Space Force), so every later game mentioning it is considered to reference the Galaxian series, unless referencing a previous game already mentioning it. Also note that if a series unrelated to Galaxian is revealed to take place in the same continuity in the official UGSF timeline, it's still not included here, since no direct link between them ever happened. See UGSF Timeline to know what games take place in its continuity.