List of Quake 1 clones on the Steam store

Abglantz (Coming soon) (Demo available)
AMID EVIL (Demo and DLCs available)
ASKE (Coming soon) (Demo available)
BRAZILIAN DRUG DEALER 3: I OPENED A PORTAL TO HELL IN THE FAVELA TRYING TO REVIVE MIT AIA I NEED TO CLOSE IT (Demo and DLC available)
BRAZILIAN DRUG DEALER BEFORE 4: DEMONS FROM THE PORTAL TO HELL I OPENED ARE STILL IN THE FAVELA AND NOW I HAVE TO SAVE MAMADAS FROM RONALDO (Coming soon)
CARNAL (DLC available)
Chasm: The Rift (Demo available)
Coven (Demo available)
Daemonic Runner
Deathmatch Classic
Devil Daggers
DISDAIN (Coming soon) (Demo available)
DOOMBRINGER (Demo available)
Dread Templar
Dusk (DLCs available)
FLESHCANCER (Coming soon)
Half-Life: Element 64 (Coming soon) (Demo available)
Hellscreen (Demo available)
Herald of Havoc
HeXen II
HROT (Demo available)
INCISION (Demo available)
KARM (Demo and DLC available)
Perilous Warp (Demo and DLC available)
Project: AMICA (Coming soon) (Demo available)
Techlie
They Came From Dimension X (Coming soon) (Demo available)
ULTRAKILL (Demo available)
WRATH: Aeon of Ruin

Optional add-ons available to download in the in-game "Add-ons" menu on Quake

Beyond Belief
Contract Revoked
Honey
Quake 64
Rubicon 2
Terra
The Punishment Due
Underdark Overbright & Copper

Let me know if i'm missing something!

Looking for more lists like this one? check these game engine lists made by Wiggy and I:
List of Build Engine games
List of Doom clones on the Steam store
List of Doom Engine games on the Steam store
List of GoldSrc Games
List of Id Tech 2 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
List of Wolf 3D clones on the Steam store