Dungeon Siege is a franchise of games developed first by Chris Taylor, in 2002. The games are built around the hack and slash/dungeon crawl basics made popular by Diablo. One of the major advantages over the Diablo games was the ability to purchase animals (mules) to allow for a much larger inventory while adventuring. The magic system was also much more diverse than that of Diablo. Kept in were many of the same addictive traits such as the replayabilty and the random loot drops. The characters develop skills based on what type of actions they take (shoot a bow often to increase your archery skill, use a certain magic to level it up faster). Also included was a co-op multiplayer that allowed for multiple people to band together to tackle the dungeons.
The original game (Dungeon Siege) was published on the PC and Mac, the stand alone expansion pack was only made available for the PC and contained the entire original game in the package. Later a sequel, with expansion pack, was released with some changes that brought the game more in line with the Diablo series. An offshoot was made exclusively for the PSP, entitled Dungeon Siege:Throne of Agony. A third game in the series, Dungeon Siege III, was released in 2011.
Toolsets have been made available to players that allow for the creation of many new adventures, or, in the case of some mods, a complete overhaul of the game or even an updates version of an older game (e.g. Ultima V: Lazarus mod for DS1).