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A month after Alpha Centauri's February 1999 release, the Firaxis team began work on the expansion pack, Sid Meier's Alien Crossfire. Alien Crossfire features seven new factions (two that are non-human), new technologies, new facilities, new secret projects, new alien life forms, new unit special abilities, new victory conditions (including the new "Progenitor Victory") and several additional concepts and strategies.
from Mega.Co.Nz (unknown size)
SidMeiersAlienCrossfire.sit (449.47 MiB / 471.3 MB)
System 7.0 - 7.6 - Mac OS 9 / compressed w/ Stuffit
Emulating this? It should run fine under: SheepShaver