One Easter egg is the Gandhi Kong game. The actual console is on the Railgun Asteroid level, in the staff lounge, and can be played (but watch your back; enemies can still shoot at you!) You play Gandhi, using the principles of passive resistance to save your village from a marauding ape.
GUNMETAL was developed and published by Mad Genius Software of Vancouver, B.C., Canada; i.e. it was self-published.