Galaxy
The original version of Galaxy was developed by Russel Wallace somewhere in 1991 or maybe even earlier (V2.9 has a 1991 copyright). To the best of our knowledge, there are no original-version Galaxy servers active.
GalaxyNG
GalaxyNG was created by Frans Slothober and introduced multiple homeworlds and partial bombings. Frans had several reasons for creating GalaxyNG. It is the variant that is most similar to original Galaxy. The people who designed Galaxy and GalaxyNG are listed in the GalaxyNG Credits.
GalaxyPlus
GalaxyPlus (G+) was developed in Russia. It is similar to GalaxyNG but has some differences. These guys take their Galaxy seriously. Some links: Unidentified Planet, News and Links, Sargona server, Lucky, PBEM Latvia, GVNG (Galaxy Viewer Next Generation, First Moscow server, The Russian Hall of Fame.
Blind Galaxy
Howard Bampton created Blind Galaxy, which provides much less information to players. Information about other races and ships is hidden until they are encountered by your own ships. New games are often announced on the galaxyng-players mailing list. Some links: Bernhard Schmidt, WWW.BLINDGALAXY.ORG.
Galaxy Explorer
Galaxy Explorer is a variant that provides very little information to players. All ships fire simultaneously, resulting in very bloody battles. It is similar to, but not based upon, Blind Galaxy.
Galaxy PBW
Galaxy PBW (play-by-web) is a variant of Blind Galaxy written in Java that is played on the web (instead of by email).
GalaxyNT
GalaxyNT was a port of GalaxyNG to WindowsNT.
Blind GalaxyNG
Blind GalaxyNG was a modification of GalaxyNG to create a game similar to Blind Galaxy.
Galaxy G
Galaxy G is extinct.
Galactica and Galaxy/2
Galactica and Galaxy/2 are extinct. They featured partial bombing, ship support and refueling, carriers and intelligent battle targetting. Galaxy/2 was the precursor to Galactica.