ZDoom may be used and distributed free of charge. No profit may be made from the sale of it. ZDoom was created by Randy Heit using id Software's and various others' sources.
Why would I want to use ZDoom instead of regular Doom?
Consider all these features that ZDoom has that are not found in the standard Doom originally released by id:
It runs well under all modern versions of Windows, from Windows 95 to the new Windows Vista. If you have Linux, it works with that too.
Can play all Doom engine games, including Ultimate Doom, Doom 2, Heretic, Hexen, and Strife.
Supports all the editing features of Hexen. (ACS, hubs, new map format, etc.)
Supports most of the BOOM editing features.
Many more all-new editing features such as:
Colored sector lighting.
Custom monsters, weapons, and items.
High resolution textures.
Many, many extensions to ACS that were not present in Hexen.
More music formats: Ogg Vorbis, MOD, XM, IT, S3M, MIDI, and MP3 as well as old-fashioned MUS all work.
More sound formats: FLAC and WAVE can both be used for sound effects.
More texture formats: PNG and JPEG are both useable for artwork.
The vast majority of Doom limits are gone.
An OPL softsynth is provided that can play the standard MUS music for an authentic 'oldschool' flavor.
Free look (look up/down).
High resolutions.
Translucency (regular and additive).
A console.
Full-featured joystick/gamepad support under Windows.
Up to 8 player network games using UDP/IP, including team-based gameplay.
Support for the Bloodbath announcer from the classic Monolith game Blood.
Quake-style key bindings.
Jumping.
Crosshairs.
Walk over/under monsters and other things.
Note: Windows download link contains the executable for Windows platforms and data files. If you need help getting started with it, see the online documentation in the wiki. You need to provide your own game IWAD. If you do not have a copy of Doom, Heretic, or Hexen, the easiest way to obtain them is to purchase them from Steam. When you download them from Steam, ZDoom will automatically find them.