Starcraft
Starcraft is a real-time strategy computer game (which includes one expansion pack) that features a world with 3 races - humans (called Terrans), a biological parasite (called zerg) and a race of teleporting superior intelligence life forms (called protoss). The game has only 2 types of resources - minerals and gas, which is one of the simplest games in terms of resource gathering. The ultimate aim of the game is to kill your opponent(s), by killing all of their creatures and destroying all of their buildings.
You start with a base, 5 gatherers (different ones for each of the 3 races) and 200 minerals. The gatherers can then either mine minerals (using the 200 minerals to buy more) and/or they can build new buildings, including a gas miner. Once buildings are made, you can hire creatures from the buildings (except for zergs, who hatch creatures from their base with eggs). Defence buildings can also be built as can new bases.
Compared to some other strategy games such as Heroes of Might and Magic, Starcraft is incredibly simple. However, Starcraft is much more popular.
Starcraft also can be played very easily over the internet, and you get free lifetime play over Battle.Net as part of buying the game. The game is still popular on the internet, with both versions of the game, although realistically you need a fast connection in order to play. Like many internet games, hacking is a major problem, although the designers have found ways to at least partially combat it.