HacX

HacX is a commercial add-on for Doom II. While it mostly retains the original gameplay formula, the plot of HacX is completely unrelated to the Doom franchise.

The protagonist of HacX is a high-profile hacker called Danny Evanger. The background story tells how he had hacked into the classified database of Genemp Corporation, a company involved in biotechnology development. The database, called GENIE, was able to block the hacking attempt, resulting in Danny Evanger's arrest and lifetime imprisonment. Without hope of ever returning to hacking, Danny takes up intensive weight training to survive the harsh prison environment. However, one day he is contacted by a government agent. A nationwide chaos has erupted, and the government suspects that an international consortium of high-tech conglomerates might be behind this. Danny's skills as the best hacker in the field are required to verify this, and his augmented physical strength should also help get the job done.

The player's objective is thus to infiltrate the corporate databases and acquire evidence of their involvement in the crisis. The gameplay is mostly the same as in Doom - you run through levels, kill monsters and search for a keycard from time to time. The levels are however more detailed and realistic, similar to Duke Nukem 3D. Some modifications were also made to the Doom II engine to allow for extensions such as destructible objects.

A distinctive feature of HacX are the "cyberspace" levels. According to the plot, Danny received from the government an implanted device called Genemp Microtel, which allows to physically travel through cyberspace. This facilitates transitions between different locations and even countries. Cyberspace levels have unique elements such as invisible floors with different elevations, and extra enemies that do not appear elsewhere in the game.

HacX has its own set of textures, sprites, sound effects and music, and does not use any of the original Doom II content. Weapons and powerups have different names and appearance, but most of them remain the same or only slightly modified compared to Doom games. Many monsters however underwent significant changes in behaviour and strength, and are very different from their Doom counterparts.