Games like Wave Defense: Trappist
Games like Wave Defense: Trappist include Total War: WARHAMMER III, FTL: Faster Than Light, Aliens: Dark Descent, DG2: Defense Grid 2, and Battlefleet Gothic: Armada (Classic). We matched them by the tags players give Wave Defense: Trappist on Steam (Strategy, Action Roguelike, Tower Defense, Space, and Real Time Tactics): closest matches first, and among equally close ones the better-known games.

Total War: WARHAMMER III
Shared: Strategy · Real Time Tactics · Fantasy

FTL: Faster Than Light
Shared: Strategy · Space · Sci-fi

Aliens: Dark Descent
Shared: Strategy · Real Time Tactics · Tactical

DG2: Defense Grid 2
Shared: Strategy · Tower Defense · Real Time Tactics

Battlefleet Gothic: Armada (Classic)
Shared: Strategy · Space · Real Time Tactics

Taur
Shared: Strategy · Tower Defense · Real Time Tactics

Creeper World 4
Shared: Tower Defense · Real Time Tactics · Strategy

Hades
Shared: Action Roguelike · Roguelite · Indie

Battlefleet Gothic: Armada 2
Shared: Strategy · Space · Real Time Tactics

Bad North: Jotunn Edition
Shared: Tower Defense · Real Time Tactics · Action Roguelike

Kingdom Rush - Tower Defense
Shared: Strategy · Tower Defense · Fantasy

Orcs Must Die! Deathtrap
Shared: Tower Defense · Strategy · Roguelite

EVERSPACE™
Shared: Action Roguelike · Space · Roguelite

Sid Meier's Civilization®: Beyond Earth™
Shared: Strategy · Space · Sci-fi

Stellaris
Shared: Strategy · Space · Sci-fi

Shortest Trip to Earth
Shared: Strategy · Space · Roguelite

Crying Suns
Shared: Strategy · Space · Roguelite

STAR WARS™ Empire at War - Gold Pack
Shared: Strategy · Space · Sci-fi

Shadow Tactics: Blades of the Shogun
Shared: Strategy · Real Time Tactics · Tactical

Defense Grid: The Awakening
Shared: Strategy · Tower Defense · Sci-fi

Necrosmith
Shared: Action Roguelike · Tower Defense · Strategy

The King is Watching
Shared: Tower Defense · Strategy · Fantasy

Element TD 2 - Tower Defense
Shared: Tower Defense · Strategy · Real Time Tactics

Orcs Must Die! 3
Shared: Strategy · Tower Defense · Action