Games like CM-SS13
Games like CM-SS13 include Arma 3, Counter-Strike 2, RUNNING WITH RIFLES, Tom Clancy's Rainbow Six Siege, and WARDOGS. We matched them by the tags players give CM-SS13 on Steam (Top-Down Shooter, Sandbox, RPG, Military, and Space): closest matches first, and among equally close ones the better-known games.

Arma 3
Shared: Military · Action · Shooter

Counter-Strike 2
Shared: Shooter · Action · PvP

RUNNING WITH RIFLES
Shared: Top-Down Shooter · Military · Sandbox

Tom Clancy's Rainbow Six Siege
Shared: PvP · Shooter · Action

WARDOGS
Shared: Military · PvP · Action

Mount & Blade II: Bannerlord
Shared: RPG · Sandbox · Action

Arma Reforger
Shared: Military · Shooter · Action

Mount & Blade: Warband
Shared: RPG · Sandbox · Military

Space Engineers
Shared: Sandbox · Space · Simulation

Rust
Shared: Sandbox · PvP · RPG

Battlefield™ 2042
Shared: Military · Shooter · Action

War Thunder
Shared: Action · Military · Simulation

Squad
Shared: Military · PvP · Shooter

PUBG: BATTLEGROUNDS
Shared: PvP · Shooter · Action

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

BattleBit Remastered
Shared: Military · Shooter · PvP

Battlefield™ 6
Shared: Military · Action · Shooter

Terraria
Shared: Sandbox · Multiplayer · PvP

Elite Dangerous
Shared: Space · Space Sim · Sandbox

Call of Duty®
Shared: Military · Action · Shooter

Holdfast: Nations At War
Shared: Military · Shooter · Action

EVE Online
Shared: Space · Space Sim · Sandbox

Star Valor
Shared: Sandbox · RPG · Space

Grand Theft Auto V Legacy
Shared: Action · Shooter · Multiplayer