Master of Orion

"Master of Orion (MoO or MOO) is a turn-based, 4X science fiction computer strategy game released in 1993 by MicroProse on the MS-DOS and Mac OS operating systems. The purpose of the game is to lead one of ten races to dominate the galaxy through a combination of diplomacy and conquest while developing technology, exploring and colonizing star systems. The game uses a point-and-click interface as well as keyboard shortcuts to control the management of colonies, technology, ship construction, diplomacy and combat. The name is a reference to the Orion system, the game universe's conquerable homeworld of a mythical race that once controlled the galaxy.

Two sequels were created, Master of Orion II: Battle at Antares in 1996 and Master of Orion III in 2003, as well as the open source freeware FreeOrion which is loosely based on the series. A prototype was developed under the name Star Lords though it was only released as freeware in 2001 as part of the promotion for MoO III.

Master of Orion was well received, and is a member of GameSpy's Hall of Fame and GameSpot Greatest Games of All Time.
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Source: Wikipedia, "Master_of_Orion", available under the CC-BY-SA License.