Keen 6 Easter eggs
This is a list of easter eggs (intentionally hidden messages and functions) in Keen 6: Aliens Ate My Baby Sitter!
The translation for the entire Standard Galactic Alphabet is hidden in the Blooglab Space Station through a secret passage off the right edge of the level. The Y + F10 cheat code can be used to reveal where the secret passage is.
In the Bloog Control Center, you can hear this Morse code playing in the background music: SOS SOS DE KEEN SOS SOS K. DE KEEN is morse-speak for "this is Keen" and K means "I am listening" (for a response).
When asked about this, Bobby Prince, the composer of the music for Keen 6, said he had never noticed this before in the game and he was not the one who put it in the song.
A possible homage to Keen 6, the status screen after every level of Wolfenstein 3D shows Billy's grandfather holding his Parabellum-Pistole similar to how Keen holds his Neural Stunner on the title screen (albeit mirrored). Both games were created by id, Keen 6 in 1991 and Wolfenstein 3D in 1992.
To Serve Man
Although not a true Easter Egg but a clever hoax is is widely believed that in the secret shaft of the Second Dome of Darkness, if you press up at a part while riding the moving platform, you'll be taken to a secret area that contains a window with a walking Commander Keen and a SGA sign that is translated as "ICU". This is because of a rather well done video.
This website also mentions this mysterious easter egg.