Games like Ancient Warfare 3
Games like Ancient Warfare 3 include Ravenfield, Garry's Mod, Totally Accurate Battle Simulator, Mount & Blade II: Bannerlord, and Arma 3. We matched them by the tags players give Ancient Warfare 3 on Steam (Sandbox, Simulation, Action, Strategy, and Indie): closest matches first, and among equally close ones the better-known games.

Ravenfield
Shared: Sandbox · War · Action

Garry's Mod
Shared: Sandbox · Moddable · Simulation

Totally Accurate Battle Simulator
Shared: Sandbox · Simulation · Strategy

Mount & Blade II: Bannerlord
Shared: Strategy · Sandbox · War

Arma 3
Shared: Action · Simulation · Shooter

Total Tank Simulator
Shared: Simulation · Sandbox · Strategy

People Playground
Shared: Sandbox · Simulation · Moddable

Ultimate Epic Battle Simulator
Shared: Sandbox · Simulation · Strategy

Freeman: Guerrilla Warfare
Shared: Action · Strategy · Sandbox

Arma Reforger
Shared: Simulation · Action · Strategy

Hot Dogs, Horseshoes & Hand Grenades
Shared: Sandbox · Simulation · Shooter

Animal Revolt Battle Simulator
Shared: Sandbox · Simulation · Indie

Kerbal Space Program
Shared: Simulation · Sandbox · Physics

BONEWORKS
Shared: Sandbox · Action · Physics

Rising Front
Shared: Sandbox · Simulation · War

Easy Red 2
Shared: Sandbox · Moddable · Singleplayer

Hell Let Loose: Vietnam
Shared: Simulation · Action · Strategy

KovaaK's
Shared: Action · Simulation · Indie

Counter-Strike 2
Shared: Action · Shooter · FPS

BeamNG.drive
Shared: Simulation · Sandbox · Physics

Arma 2: Operation Arrowhead
Shared: Simulation · Action · Strategy

Cities: Skylines
Shared: Simulation · Sandbox · Strategy

Hell Let Loose
Shared: Shooter · Action · War

Goat Simulator
Shared: Simulation · Sandbox · Action