Executable hack

A executable hack, also known as a exe hack, is a modification of the executable that is shipped with Doom, Doom II, Heretic or Hexen. The term usually denotes a modification made by fans, as opposed to any of the officially licensed versions produced by id Software or affiliated companies. Unlike a source port or a source modification, they apply their changes directly to the executable and are usually made to raise limits as opposed to removing them.

Although exectuable hacks are a rarity, they continue to be made by a small but selected group of authors knowledgeable enough to direct modify the executable.

History
Executable hacks originated in the early to mid 2000's. They were seen as an option to retain complete vanilla and demo compatibility yet still raise several static limits within the executable, such as or. An intimate knowledge of is often needed to create the necessary patches to apply to the executable. A specialized program called exists that creates  files that can be used for this very purpose, although other patches come in the form of pure source code.

Unlike source ports or modifications, executable hacks are nearly always based off the vanilla executables, namely: They are not derived from the original Linux Doom source code.
 * DOOM.EXE
 * DOOM2.EXE
 * HERETIC.EXE
 * HEXEN.EXE

Executable hack versus source modification
The differences between a executable hack and a source modification lay in the nuances they make and the intents of their purposes:
 * A executable hack is meant to raise the limits offered by the original executable and retaining full compatibility.
 * A source modification  includes new additions that are meant for a specific goal in mind, providing a subset of new features that aren't enough to warrant the source port moniker.
 * Executable hacks do not come with source code, as they are based directly on the game's executable. Several executable hacks come in the form of specific patches such as files.

List of executable hacks
As a high level of programming knowledge is required to create a executable hack they are less in numbers than source modifications or source ports. A summary list of executable hacks is provided below.

Doom

 * Doom-plus
 * Master
 * Nr4tl
 * Sigexe
 * F2DoomPP

Doom 2

 * Doom2-plus
 * Doom32

Heretic

 * Heretic-plus
 * vvHeretic
 * CHeretic

Hexen

 * Hexen-plus
 * CHexen