OpenOffice (included games)

To invoke the Space Invaders clone, the player first enters the data

=game()

into a cell. The contents of the cell then change to "say what?", whereupon the player enters further data there:

=GAME("StarWars")

This becomes more difficult on subsequent sessions, where the cell instead recites a quote from The Hitchhikers' Guide to the Galaxy, "oh no, not again!"