Games like Append
Games like Append include Counter-Strike 2, HELLDIVERS™ Dive Harder Edition, Deployment, HELLDIVERS™ 2, and Marathon. We matched them by the tags players give Append on Steam (Action, Shooter, Multiplayer, Gun Customization, and Twin Stick Shooter): closest matches first, and among equally close ones the better-known games.

Counter-Strike 2
Shared: Shooter · Multiplayer · Action

HELLDIVERS™ Dive Harder Edition
Shared: Action · Twin Stick Shooter · Multiplayer

Deployment
Shared: Shooter · Action · Multiplayer

HELLDIVERS™ 2
Shared: Multiplayer · Shooter · Action

Marathon
Shared: Multiplayer · Shooter · Action

The Ascent
Shared: Action · Shooter · Top-Down Shooter

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

PUBG: BATTLEGROUNDS
Shared: Shooter · Multiplayer · Action

Call of Duty®: Black Ops III
Shared: Multiplayer · Shooter · Action

STAR WARS™ Battlefront™ II
Shared: Shooter · Multiplayer · Action

Titanfall® 2
Shared: Multiplayer · Shooter · Action

Apex Legends™
Shared: Multiplayer · Shooter · Action

Strike Force Heroes
Shared: Action · Shooter · Multiplayer

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

Halo: Spartan Assault
Shared: Action · Shooter · Top-Down Shooter

Broforce
Shared: Action · Multiplayer · 2D

Battlefield™ 2042
Shared: Shooter · Multiplayer · Action

RUINER
Shared: Action · Top-Down Shooter · Twin Stick Shooter

Team Fortress 2
Shared: Multiplayer · Shooter · Action

Call of Duty®
Shared: Shooter · Multiplayer · Action

ShellShock Live
Shared: Multiplayer · Action · Shooter

PAYDAY 2
Shared: Action · Multiplayer · Shooter

Borderlands 2
Shared: Shooter · Action · Multiplayer

Ready or Not
Shared: Shooter · Multiplayer · Action