The Goodbye, Galaxy! series is part of the Commander Keen series comprising of two titles; Commander Keen Episode IV: Secret of the Oracle and Commander Keen Episode V: The Armageddon Machine. Episode IV was released under the Shareware model; you buy the title for a small fee and then decide you want the next. Episode V was priced at full price.
The two games are set after the Invasion of the Vorticons series which was followed by Keen Dreams. The games feature improved graphics over the Invasion series, and also sport a game of pong.
