Hottest free UNIX "4X" games

GAME GENRE – 4X games are strategy games built around four simple ideas: eXplore, eXpand, eXploit, and eXterminate. In other words, you explore the world, expand your empire, exploit its resources, and eventually explain to your neighbors why their capital would look better under new management. Players typically discover new territories or planets, research technologies, build cities and armies, manage resources, and wage war against rival civilizations. Some games focus heavily on diplomacy and economics, while others are perfectly happy to let you solve every problem with an enormous fleet of spaceships.