I will upload any future mutators here for the ZDoom community to enjoy!
RealAim • realAim.pk3
Adds scripted camera inertia and additional movement bobbing that affect your aim and give your overall movement a less mechanical feeling.
Dark Doom • dark_doom.pk3 - Updated 11/28
Screenshots using Dark Doom Black, Dark Doom Flashlight 2.0, and Subdued Lights. Tonemap: Uncharted 2, Bloom: On


Click to enlarge.
Simple scripted mutator that lowers light levels in practically any (G)ZDoom environment.
Dark Doom Lite • dark_doom_lite.pk3 - Slightly brighter; for enhancing already dark maps. - Updated 11/28
Dark Doom Black • dark_doom_black.pk3 - Complete darkness except for special sectors; flashlight / nightvision required! - Updated 11/28
Dark Doom Flashlight 2.0 • dd_flashlight2.0.pk3 [Updated 11/26/2016]
Scripted beam flashlight; uses ACS instead of projectiles to instantly place a beam and prevent lag.
Subdued Lights • subdued_lights.pk3
Dynamic light definitions that cover double the area at half brightness (Doom only).
Super Ultimate Realism v1.0 • superUltRealism_1.0.pk3
The pinnacle of modular realism enhancment mutators; just add this to almost any ZDoom mod or game to bring the experience to the next level!

Drunk Doom • drunk.pk3
Scripted camera and motion effects that get stronger the higher your health is; this mutator replaces Doom's health pickups with various forms of booze.