Sid Meier's Civilization: The Board Game (thing)
In 1981, Avalon Hill released a board game called Civilization. In it, each player took control of an ancient civilization and guided it through history, researching technologies, building cities, and making war. In 1991, Microprose released a videogame called Sid Meier's Civilization, which had much the same premise and seemed to borrow a number of gameplay elements from the boardgame. (More details about this can be found in the Civilization node.) This videogame spawned two (or perhaps three, depending on what you count) sequels, simply named Civilization II and III.
Naturally, the game is vastly simplified from the computer game, though a suprising number of concepts from it are translated into this board game version. Players still build cities, settlers, and military units; they still explore the map; they still research technologies; they still develop their cities, whether by causing them to grow in size or building improvements in them; and they still collect and trade resources. All four of the so-called "four Xes" of empire-building games are preserved: expansion, exploration, exploitation, and extermination.
The greatest simplification from the computer games is the reduction of the various resources like food, shields, and commerce into one resource: money. Cities produce money every turn, and players buy things with it. Cities grow by buying the upgrade, units are produced by buying them, technologies are researched by paying their cost, and so forth.
The biggest gripe with the game I have is with the pieces, and my complaints are two-fold. First, every player shares the same color of military units. While each player has their own color of plastic pieces for their cities and settlers, the only way to signify which player a given army belongs to is to use one of the helpfully provided flagbearer units each player also has. This can make certain situations difficult to keep track of, like when two players each have an army inside of a territory at the same time (in such a situation, a battle will not occur if both players agree not to fight; thus, two players can defend against a third). The second gripe I have is with the quality of the pieces. The vast majority of them are just fine, but a few have some pretty fragile bits, like the settler's walking stick, and the spearman's spear.
The game is divided into four eras, like the computer game: ancient, medieval, industrial, and modern. As players discover new technologies, old units gain upgrades, and new, better units become unlocked. There are five basic types of military units: three basic land units, fleets, and aircraft (which don't get unlocked until the modern era). The three basic land units are infantry, cavalry, and artillery, which are arranged (in the battle system) in a rock, paper, scissors sort of way, which adds an interesting twist to both strategy (if a player has a lot of a certain type, you'll want to build units of the type that has an advantage against it) and tactics (if you're fighting a battle, you'll want to keep track of what the other guy's unit balance is, and choose your own units accordingly).
A player's cities are kept track of by special city cards. Each city a player has gets a card, which keeps track of how much that city produces and what size it is (since cities can be up to size 4, this works out nicely for a four-sided card; each edge of the card signifies a different size of city).
The game comes with a number of tokens, which signify different types of territories. One is placed, face-down, at random, on each territory when starting the game. Some tokens denote resources, which give cities bonuses to production. Some give immediate bonuses to players when discovered, like a free technology or free money. Some do bad things, like limiting the maximum size of a city built in that spot, or unleashing a plague that kills units. (The size of the plague increases as the game progresses; if, somehow, an undiscovered plague token lasts until the modern era, it can potentially wipe out an area the size of Asia when discovered. In the ancient era, when it's most likely to be discovered, it only affects the territory it's found in.) Some simply do nothing.
The game uses an ingenious system for player turns. One annoying thing about other games of this sort is that player turns can take a long time. (Axis & Allies is a good example.) So, instead of having each player play their entire turn all at once, each player takes their turn during each phase. So first is the purchase phase, where each player buys things in turn. Then is the movement phase, when each player moves and battles in turn. Third is the trade phase, where each player trades resources, money or anything else (including cities, units, and technologies) with the other players. And last is the production phase, where each player adds up the amount of money they get for that turn and collects. Then this cycle is repeated again, except that the person who goes first in each phase changes to the next person on the left; in this way, no one gets a serious advantage by going either first or last in every turn. This also means that each player has a much shorter wait during times they get to do nothing.
I have played this game several times, both with fans of the computer game and people who have never even heard of it. As with any big board game (and I mean big: the board measures 36" by 46") of this sort, it is not recommended for the impatient or the especially young. The rules are not particularly difficult, particularly if you and the people you play with have played either the computer game or other board games on this level of complexity (which I would put on a level with Axis & Allies). The rule book does have both "standard" and "advanced" rules, but the standard rules are so mind-numbingly simple that they almost don't bear mentioning. One downside is that games last terribly long, to the point where if you aren't prepared to dedicate an entire table to this game for a period of days, you should maybe think about something shorter.