Games like Space Wars: Interstellar Empires
Games like Space Wars: Interstellar Empires include Dota Underlords, Touhou Big Big Battle, Yu-Gi-Oh! Master Duel, VRChat, and Infinity Wars: Animated Trading Card Game. We matched them by the tags players give Space Wars: Interstellar Empires on Steam (Early Access, Free to Play, Massively Multiplayer, Tactical, and Strategy): closest matches first, and among equally close ones the better-known games.

Dota Underlords
Shared: Free to Play · Strategy · Tactical

Touhou Big Big Battle
Shared: Early Access · Massively Multiplayer · Strategy

Yu-Gi-Oh! Master Duel
Shared: Free to Play · Strategy · Turn-Based Tactics

VRChat
Shared: Free to Play · Massively Multiplayer · Early Access

Infinity Wars: Animated Trading Card Game
Shared: Free to Play · Strategy · Tactical

Dota 2
Shared: Free to Play · Strategy · Free To Play

World of Warships
Shared: Free to Play · Strategy · Massively Multiplayer

Arena Breakout: Infinite
Shared: Free to Play · Tactical · Massively Multiplayer

Transformice
Shared: Free to Play · Massively Multiplayer · Strategy

Eternal Card Game
Shared: Free to Play · Strategy · Massively Multiplayer

Star Trek Online
Shared: Free to Play · Massively Multiplayer · Space

SMITE®
Shared: Free to Play · Strategy · Massively Multiplayer

Warframe
Shared: Free to Play · Massively Multiplayer · Space

PUBG: BATTLEGROUNDS
Shared: Tactical · Massively Multiplayer · Early Access

BLOCKPOST LEGACY
Shared: Free to Play · Massively Multiplayer · Early Access

FTL: Faster Than Light
Shared: Strategy · Space · Indie

LuckCatchers
Shared: Free to Play · Massively Multiplayer · Strategy

Limbus Company
Shared: Free to Play · Turn-Based Tactics · Strategy

XCOM 2
Shared: Strategy · Tactical · Turn-Based Tactics

Delta Force
Shared: Free to Play · Massively Multiplayer · Free To Play

中华三国志 the Three Kingdoms of China
Shared: Free to Play · Strategy · Indie

Order of Battle: World War II
Shared: Free to Play · Strategy · Hex Grid

Demise of Nations
Shared: Free to Play · Strategy · Indie

Bodycam
Shared: Tactical · Early Access · Massively Multiplayer