Mods for games have been around since the first programmer opened a game to look inside the code how it worked. Many modmakers have even gone to become part of the industry, making games themselves.
In the Diablo franchise, there's mods for Diablo I and Diablo II, and loads of skilled fans waiting to get their hands on Diablo III.
A mod refers to a a modified version of a game, usually a player-made version of the game with various added features or gameplay changes. Such games are generally referred to as "mods." Some people mistake these for cheats and hacks, which they are not! A mod will alter gameplay much more than a simple hack would.
The rich history of mods has been added to the DiabloWiki, and is available for anyone to read. Information about individual mods like Median XL by Brother Laz or the Eastern Sun as well as modding history or modding tips can be found on the main modding article:
Read more about different modifications to the Diablo games on the Mod article.