This page is for the original game. For the 2016 game, see Doom (2016).
A list of all alpha, beta, and shareware versions of the game can be found at Doomworld Shareware section. Details about each alpha and beta release can be found both on The Page of Doom and the Doom Wiki. Note that the .WAD files available in the alphas and beta are not compatible with any Doom source port.
Since the release of the source code, several modified engines have emerged.
You can view a more exhaustive list on Wikipedia or a set of comparison tables on DoomWiki.org. The history of various source ports is examined on Doomworld.
A freely redistributable replacement of DOOM-like assets is available at Freedoom, forming a completely free and open source game. Art assets from the original game such as the levels, sounds, textures, etc., remain under copyright. They can be purchased from Steam or copied from an original game disk.
ZDoom seeks to support multiple monitors out of the box since version 2.5.0. Widescreen Gaming Forum discusses multimonitor set ups with GZDoom.
Depending on your choice of engine, you can usually change the field of view with a console command, or even in the options. Try fov <1-179> or gr_fov <1-179>.
Run the program as administrator