battleMETAL
BRAZILIAN DRUG DEALER 3 (Early Access) (DLC Available)
Ctesiphon (Coming Soon)
DOOMBRINGER (Demo available) (Early Access)
HeXen II (Demo available)
J.A.C.K. (Includes Quake map creator)
Meadow Fun!! (FREE)
MeowGun: Hell Denizen (Demo Available) (Early Access)
Midnight Guns (Coming Soon)
Nexuiz (Previously on the Quake Engine, now on CryEngine3) (Workshop support)
Object N (FREE)
Quake (Enhanced) (Includes Scourge of Armagon & Dissolution of Eternity) (Additional Mission Packs* & Featured Add-ons** included)
Steel Storm: Burning Retribution (Demo available) (DLC available)
RetroBlazer (Coming Soon)
Station 37
THREAT VECTOR (Coming Soon)
Voidwalker (Coming Soon)
WRATH: Aeon of Ruin
WRATH: Aeon of Ruin VR (Coming Soon)

*Additional Mission Packs: Dimension of the Past & Dimension of the Machine
**Featured Add-ons: Beyond Belief, Deathmatch Dimension, Honey, QDOOM, Quake 64, Rubicon 2, Slave Zero X: Episode Enyo, Spiritworld, Tainted, Terra, and Underdark Overbright & Copper

Abaddon (Coming Soon)
Alien Arena: Warriors Of Mars (DLC available) (Workshop support)
Anachronox
AQtion (FREE)
Daikatana
Gravity Bone (FREE)
J.A.C.K. (Includes Quake II map creator)
Kingpin - Life of Crime (Unity version: Kingpin: Reloaded)
Nosferatu: The Wrath of Malachi
Quake II (Enhanced) (Includes The Reckoning & Ground Zero) (Additional Mission Packs included) (Grants the full game for Quake II RTX)
Quetoo (Unavailable, previously accessible through Greenlight)
SiN Gold (Includes SiN Multiplayer) (Remaster: SiN Reloaded)
Thirty Flights of Loving
Warfork (FREE) (Early Access) (DLC available) (Fork of Warsow)

*Additional Mission Packs: Quake II 64 & Call of the Machine

Let me know if I am missing something!

In the meantime, check out these other game engine guides by edgdangon1 and I!
List of Build Engine games
List of Doom Engine games on the Steam store
List of GoldSrc Games
List of Id Tech III games
List of Id Tech 4 games
List of LithTech games
List of Unreal Engine 1 games
List of Unreal Engine 2 games
List of Unreal Engine 3 games on the Steam store
List of Wolf 3D Engine games on the Steam store