Modification is the art of applying change to the original.
Mod or modification is also a term generally applied to computer games, especially first-person shooters such as Quake, DOOM and Half-Life, but also to real-time strategy games such as Warcraft III and the Command & Conquer; series. Mods are made by the general public, and are entire new games upon themselves. They can include new items, weapons, characters, enemies, models, modes, textures, levels, and story lines. They also usually take place in unique locations. They can be single-player or multiplayer.
A great many do not progress very far and are abandoned without ever having a public release. Some are very limited and just include some gameplay changes or even a different loading screen, while others are total conversions and can modify content and gameplay extensively. A few mods become very popular and convert themselves into distinct games, with the rights getting bought and turning into an official modification.
Among popular mods, none is more well known than the Half-Life multiplayer mod Counter-Strike, which was released shortly after the original game, and upwards of 1 million games per day are hosted on dedicated servers. Counter-Strike is probably the best example of a modification that turns into a retail game.
Mods in general are required to be open source (free) if they include any parts from another mod, or the main game.
Action Realism - Players are realistically crippled depending on where they are shot. They also lose energy if they have open wounds, and must stop to apply bandages.
Akimbo Arena - Allows players to use two of any weapon, one in each hand.
Infiltration - Realism modification featuring modern day military weapons and scenarios.
Instagib - All players have high-powered Shock Rifles that can blow an opponent apart with a single hit.
Call to Arms - Another total conversion bringing modern warefare to the Generals engine. There are four new sides, the USA, UK, United Arab Nations, and Russia, each with the most modern equipment that that country has to offer. The mod is semi-realistic, although not on the scale of True War II.
