Goodbye, Galaxy! is the name given to the second installment of the Commander Keen series. It consists of:
Because of the similarities between the engines (they are almost identical), Aliens Ate My Baby Sitter! is often included as part of the Goodbye, Galaxy! "trilogy", particularly with Goodbye Galaxy modding tools, which can often edit Keen 6 as well.
In the storyline though, Aliens Ate My Baby Sitter! sits well and truly after the Goodbye, Galaxy! series, although some elements of the Goodbye, Galaxy! story do continue in Aliens.
The Invasion of the Vorticons series precedes Goodbye, Galaxy! and Keen Dreams is often considered to fit in between these two series because its look and feel can be seen as being something of a halfway point between them, particularly in its introduction of the isometric style of platforms (see Invasion of the Vorticons article for more on this).
A hint sheet was released with the registered versions of the games in this series, which contains tips, cheats and other interesting information.