BioShock is a series of first-person shooter video games by Irrational Games, all of which have to date been published by 2K Games. All the games in the series are unique not just for their priority on their stories over shooting, but also for their great emphasis on exploring various political concepts. The main setting for most of the games is in a seastead environment, with the exception of Bioshock Infinite, which inverts this in a more upwards direction.
Fair warning to anyone who hasn't played any or all of the BioShock games: there are huge spoilers ahead.
The video game BioShock features what is probably the best-known example of a seastead in popular culture, and serves as a scathing criticism of Objectivism. Its setting, known as Rapture, is an undersea city in the Atlantic Ocean built between 1946 and 1951 by billionaire industrialist and White Russian exile Andrew Ryan, acting as a place where the "best and brightest" can live free from the heavy hands of big gummint, organized religion, and the scornful untermenschen that want to restrict them, and where they could ride out the nuclear war that Ryan saw as inevitable. There, they would build a society run in accordance with logic and rationalism, where brilliant artists, scientists, engineers, and captains of industry can live their dreams and fulfill their true potential. In practice, this meant Objectivist principles, the city serving as a version of Galt's Gulch. Everything is privately owned, from the transit systems and production of food and fresh water up to and including the oxygen supply. Also like Galt's Gulch, Rapture would be kept secret from the world so as to prevent it from being attacked by NATO or the Soviets.
It goes about as well as any sane human being would expect it to, as society grows heavily stratified between the elites and the workers that they brought in to maintain their utopia. Said elites cynically abandon their original ideals in their quest to stay in power, effectively becoming the very government that they had rebelled against. Mad artists murder and mutilate people in the name of their horrifying "art," and take "freedom from censorship" to mean "freedom from any and all criticism by those too stupid to recognize my artistic brilliance!" Medical professionals by and large take to throwing the Hippocratic Oath out the window, instead performing horrific experiments on their patients for the sake of profit and ego. Critics of those in power find themselves unable to get their message out because all of the media and "public" venues are owned by those very leaders. All religion is outlawed, and missionaries attempting to smuggle Bibles into Rapture are executed. A New York gangster named Frank Fontaine infiltrates the place and builds a criminal empire through his smuggling contacts with the outside world, as well as by creating an unscrupulous biotech company that's more concerned with money than ethics. He harnesses working-class resentment to start a civil war in his pursuit of getting rich, ironically living up to the principles of Objectivism far better than the self-serving leadership — the war started because Ryan nationalized his company and cracked down on his smuggling.
The tipping point comes with the discovery of ADAM. A viscous green liquid derived from a species of sea slug native to the seabed near Rapture, ADAM turns out to have powerful medical properties and utility for genetic engineering. Lack of regulation means that it is quickly put to use in the most decadent manners possible, before its side effects and addictive properties become fully known. Extra attention is paid by researchers on ADAM's offensive utilities, as people use it to give themselves superpowers. While there aren't enough of the sea slugs to make ADAM commercially viable on their own, it is soon discovered that that implanting them into the stomach of a human being, specifically that of a young girl, allows the slug to produce massive quantities of the stuff. As a result, orphaned girls are kidnapped and parasitized in order to harvest ADAM in commercial quantities, guarded by the most heavily-armored brutes in the city, produced by taking impoverished men and grafting their genetically-augmented bodies into a diving suit while breaking their minds in the process. Neither the "Little Sisters" nor their "Big Daddy" guardians ever consented to their fates. In short, ADAM represents a worst-case transhumanism scenario, one where a genetic arms race emerges while the populace grows addicted to the stuff.
In the end, Rapture's power structure becomes based not on wealth and influence, but on personal power and the ability to kill. A mix of growing working-class discontent and rampant abuse of ADAM gone horribly wrong precipitate a civil war on New Year's Eve 1958, from which Rapture never recovers. By the time the game proper starts in 1960, everything has gone to hell. Genetically-augmented and heavily armed citizens roam the city, scavenging whatever dwindling supplies they can procure. Rapture's civilization has collapsed from lofty Objectivist ideals into an endgame of "might makes right" and "kill or be killed".
Based on their behavior throughout the game, players can determine whether or not they can follow the selfish philosophy of Rapture and seize power for themselves. Needless to say, the more selfish and powermongering players act, the worse the ending is.
 BioShock 2
While BioShock explores how a society based solely on selfishness tends to eat itself alive, BioShock 2 switches this up and looks at how even acting in a radically opposite fashion to that can result in equal amounts of horror.
By 1960, Rapture has fallen into chaos and decay thanks to both the civil war and most of the population having been driven insane due to the long-term effects of uncontrolled gene splicing. By the second game, set in 1968, the survivors have overthrown the "captains of industry" that once led them and instead turned to extreme collectivism of a sort that would leave Pol Pot feeling a mix of disbelief and admiration. Their leader, Sofia Lamb, preaches about the necessity of pure, absolute altruism, and works to indoctrinate her followers, ominously named "The Family", into abolishing free will in the name of equality. She plans to do so by conditioning her daughter Eleanor to be the living embodiment of this idea.
 BioShock Infinite
BioShock Infinite, meanwhile, takes seasteading and instead puts it in the air (skysteading, if you will). Around the turn of the 20th century, the United States builds a floating city/World's Fair called Columbia to serve as a demonstration of American power and ingenuity, only for it to go rogue and disappear. The people who took it over went on to build a society rooted in hyper-religiosity, American exceptionalism, dominionism, and virulent racism. In Columbia, WASPs are the dominant ethnic group, worshiping America's Founding Fathers as divinely-inspired figures (sound familiar?) and the city's ruler, Zachary Hale Comstock (taking his name from Anthony Comstock), as an all-knowing prophet on par with Jesus Christ. Comstock and his followers have taken to viewing the old US as having fallen into a tyranny of progressivism, abolitionism, and "mud rule", while Columbia's underclass of blacks, Irish, and other "lesser races" toil in conditions of virtual slavery (their "natural place" in the eyes of the elite) in the factories producing Columbia's weapons and luxuries. Much as in Rapture in the first two games, this eventually produces a reaction in the form of the Vox Populi, a band of communists of the militant, angry, revolutionary variety. There's also a smattering of quantum physics and multiverse theory, handled surprisingly well for a fictional property.
On a humorous note, a promotional image of the game tends to be passed around by conservative anti-immigrant groups as a sort of factual piece. It shows George Washington as a divine figure, with an angel and a halo of light behind him, hand-delivering the Constitution while surrounded by cringeworthy ethnic stereotypes of Africans, Asians, Mexicans, Irish, and Native Americans, with a caption reading "It Is Our Holy Duty to Guard Against the Foreign Hordes". These groups seem to have taken to using this image unironically, seemingly having missed the point that the image (just like the game itself) was created specifically to mock them.
Less funny is the cover art, which has drawn some criticism for feeling as though it was designed by committee and not reflective of the game as a whole. Most important is the absence of Elizabeth, the co-protagonist of the game along with the player character Booker DeWitt. However, the cover can be flipped in order to display a much better, more stylised piece of art, while the "Complete Edition" rerelease of the game proudly features Elizabeth next to Booker.