Phase 1 and Freedoom: Phase 2, and FreeDM, which contains a collection of deathmatch levels. Freedoom does not require any source port to run, and can run on any limit-removing source port of Doom. A similar project, Blasphemer, aims to create a complete free version of Heretic, but is less fully developed than Freedoom. Zauberer was also been initiated for Hexen. Editing Many level editors are available for Doom. The original Doom Editing Utility (DEU) was ported to a number of operating systems, but lost significance over time; many modern Doom editors still have their roots in DEU and its editing paradigm, including DETH, DeePsea, Linux Doom Editor, and Yadex and its fork Eureka. Other level editors include WadAuthor, Doom Builder (released in January 2003), and Doom Builder 2 (released in May 2009 as the successor to Doom Builder). Some Doom level editors, such as Doom Builder and Doom Builder 2, feature a 3D editing mode. As of now, these two have been discontinued, but a newer fork has been released and is regularly updated, known as GZDoom Builder. GZDoom Builder is also discontinued and is now being maintained as Ultimate Doom Builder. Many specialized Doom editors are used to modify graphics and audio lumps, such asXWE, SLADE, Wintex, and SLumpEd. The DeHackEd executable patching utility modifies monsters, items, and weapon behavior. In ZDoom, users can create new monsters, weapons, and items through a scripting language called DECORATE, made to address many of the shortcomings of DeHackEd, such as not being able to add new objects, and not being able to deviate far from the behavior of the original weapons and monsters. WAD2 and WAD3 In Quake, WAD files were replaced with PAK files. WAD files still remain in Quake files, though their use is limited to textures. Since WAD2 and WAD3 use a slightly larger directory structure, they are incompatible with Doom. References Bibliography Joseph Bell, David Skrede: The Doom Construction Kit: Mastering and Modifying Doom, Waite Group Press (April 1, 1995), Richard H. "Hank" Leukart, III: The Doom Hacker's Guide, Mis Press (March 1, 1995), Steve Benner, et al.: 3D Game Alchemy for Doom, Doom II, Heretic and Hexen, SAMS Publishing (1996), Kushner, David: Masters of Doom: How Two Guys Created an Empire and Transformed Pop Culture, Random House Publishing Group 2003, ; pages 166–169 Larsen, Henrik: The Unofficial Master Levels for Doom II FAQ, version 1.02 (retrieved