X-COM: Apocalypse was the third game in the XCOM franchise, following "X-COM: Terror from the Deep". It was released by Mythos Games and MicroProse in 1997 for PC (Windows and DOS).
This game was set in 2074, some thirty years after the war against the oceanic aliens, and followed the people of the self-contained city of Mega-Primus as they battled extra-dimensional aliens. The game featured fourteen different races of alien beings, some of which were dependent on each other. The game made significant use of the concept of the alien life cycle for the plot mechanism.
It was followed by "X-COM: Interceptor" which was in fact a narrative prequel.