Games like Z.A.R.
Games like Z.A.R. include Counter-Strike, Half-Life, Half-Life 2, Half-Life: Opposing Force, and Black Mesa. We matched them by the tags players give Z.A.R. on Steam (Action, FPS, First-Person, Shooter, and Classic): closest matches first, and among equally close ones the better-known games.

Counter-Strike
Shared: Action · FPS · Shooter

Half-Life
Shared: FPS · Classic · 1990's

Half-Life 2
Shared: Action · FPS · Classic

Half-Life: Opposing Force
Shared: Action · FPS · Classic

Black Mesa
Shared: FPS · Action · First-Person

Quake
Shared: FPS · Action · Classic

DOOM + DOOM II
Shared: FPS · Action · Classic

DOOM
Shared: FPS · Action · Shooter

Call of Duty®
Shared: FPS · Action · Shooter

Half-Life: Blue Shift
Shared: Action · FPS · Shooter

BioShock Infinite
Shared: Action · First-Person · FPS

Counter-Strike: Condition Zero
Shared: Action · FPS · Shooter

Halo: The Master Chief Collection
Shared: FPS · Classic · First-Person

Counter-Strike: Source
Shared: FPS · Action · Shooter

DOOM 64
Shared: Action · FPS · Classic

Apex Legends™
Shared: FPS · Shooter · First-Person

PUBG: BATTLEGROUNDS
Shared: Shooter · FPS · Action

STAR WARS™ Battlefront II (Classic, 2005)
Shared: Action · Shooter · Classic

Call of Duty® 4: Modern Warfare® (2007)
Shared: Action · FPS · Shooter

Quake II
Shared: FPS · Action · Classic

Duke Nukem 3D: 20th Anniversary World Tour
Shared: FPS · Action · Classic

Aimlabs
Shared: FPS · Action · Shooter

Battlefield™ 2042
Shared: FPS · Shooter · Action

Team Fortress Classic
Shared: Action · FPS · Shooter