GrbDoom

GrbDoom was a unfinished source modification of ZDoom 1.20. It introduced several new features that changed weapon and monster attacks extensively for experimental purposes by its creator, Jan Cholasta (Grubber).

History
The first release was based off ZDoom 1.20 and was a private release build done in either 2003 or early 2004. It remained unreleased till January 2021. The first public reveal was on June 1, 2004, when Grubber revealed GrbDoom, as version 2 with a build date of May 30, 2004. It was upgraded to ZDoom 1.23 beta 33. It implemented a new menu, Grubber Options, where the behavior of the players weapons can be changed and where also the monster's modi of attacks could be changed simultaneously.

Features
GrbDoom implements a new menu entry called Grubber Options. These consist of the following submenu's:

Weapon options
Weapon options alter the properties of the player's weapons. Multiple changes can be active at the same time. The following properties can be changed:
 * Fist: Thrust hits thing, allows the player to punch monsters in the air. When using a berserk patch, they are sent across the level.
 * This also allows the player to punch barrels in the air
 * Chainsaw: The ability to throw a chainsaw into a enemy, causing damage. When the chainsaw is dropped, the player automatically switches to the fist and the chainsaw can be picked up again
 * Pistol: Allows for a three shot burst, explosive ammunition and a bullet spread similar to a shotgun blast
 * Shotgun: Gives the ability to shoot automatically, explosive shells and the ability to change the spread in which the pellets are fired
 * Super shotgun: Similar to the shotgun, except you also gain the ability to fire a single shell
 * Chaingun: Ability to use shotgun shells as ammo, explosive bullets, and bullet spread
 * Rocket launcher: Allows for killable rockets, guided rockets, bouncing rockets which make it a grenade launcher instead, and a rocket spread similar to a shotgun spread. In addition to this, the rocket launcher can act as multiple other weapons:
 * Flamethrower: Shoots a cloud of fire. The above combinations can be applied
 * Napalm launcher: Shoots a napalm rocket whose trails are flammable costing 10 rocket ammo. The above combinations can be applied
 * Nuke launcher: Shoots a nuclear rocket which upon impact explodes in a mushroom cloud, with waste falling nearby damaging other enemies costing 10 rocket ammo. The above combinations can be applied
 * Plasma gun: Allows for killable plasma bursts, bouncing plasma bursts which make it a plasma grenade launcher instead, and a plasma spread similar to a shotgun spread. It also allows you to shoot either green or blue plasma. Several types of ammunition are provided: Normal plasma and MIRV plasma with separate plasma bursts upon impact. In addition to this, the plasma gun can act as an alternative weapon:
 * Railgun: Shoots a hyper-velocity slug with particles costing 20 plasma ammo
 * BFG9000: Can fire BFG blasts in a spread, bouncing BFG balls which make it a BFG grenade launcher instead, killable BFG blasts, and bobbing
 * In addition, it can also function as a mini-BFG shooting BFG blasts with a far higher rate of fire, at the cost of doing lower damage and having a lower spread

For weapons that use bullets or shells, shell casings can be turned on as a separate, universal feature. In addition to these changes, the weapons from Duke Nukem 3D and  are also included.

Monster options
Monster options change the weaponry of the monster's weapons. The cycle speed on which the weapons fire is retained. Multiple changes can be active at the same time. All of the following monsters can have the following properties changed:
 * zombieman, shotgun guy, imp, lost soul, cacodemon, baron of Hell, cyberdemon, spiderdemon, heavy weapon dude, Hell knight, revenant, mancubus, arachnotron, pain elemental and Wolfenstein SS:
 * The ability to fire a pistol, shotgun, super shotgun round, a chaingun bullet, a rocket, a plasma shot, a BFG shot, the plasma from an arachnotron, the slimeball from a baron of Hell or a cacodemon, the fireball from an imp, mancubus or revenant, a lost soul, the leap of a lost soul, a railgun or a rocket spread
 * Being a unfinished modification, the demon, spectre, Commander Keen and arch-vile behaviors remain unchanged

Behavioral changes can be stackable. For instance, a Hell knight can be changed to fire a lost soul that can shoot a BFG blast. Similarly, a lost soul can be changed to summon a lost soul, which summons another lost soul indefinitely. Through these parameters, a large range of combinations are possible. All monster and weapon behavior can be changed simultaneously and dynamically, as in, a restart of the map is not required for the change to be made active.

Demonstration map
The GrbDoom package includes a WAD called. It features a demonstration map that includes the following:
 * The level features a giant pyramid from which multiple monster spawners generate new monsters that roll off the sides of the pyramid
 * Transparent monsters that fade in and out of visibility
 * A static cannon that can shoot cannonballs with the power of a rocket towards enemies, essentially functioning as a turret

Legacy
In early May 2020, the author of the modification was approached through a private message on the ZDoom forums. When initial responses panned out, a public request was made in late May requesting retrieval without success.

On December 7, 2020, Grubber released version 1 of GrbDoom on GitHub, before publically releasing the latest version on January 2, 2021. The old source code was retrieved and a fresh compilation of both versions was made by Grubber before hosting it on GitHub.