Disable mouse in settings then run this. Source for hack available here.
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.
The following wads are designed to fix some sort of game data bug or a feature short coming of the game. They do not add any levels/change play style and thus are generally compatible with most user addons.
A freely redistributable replacement of Heretic-like assets is available at Blasphemer, 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.
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>.