Games like Red Planet Rampart
Games like Red Planet Rampart include Kerbal Space Program, Avorion, SPORE™, SpaceBourne 2, and Space Engineers. We matched them by the tags players give Red Planet Rampart on Steam (RPG, Space, Building, Casual, and Mars): closest matches first, and among equally close ones the better-known games.

Kerbal Space Program
Shared: Space · Building · Sandbox

Avorion
Shared: Building · Space · Sandbox

SPORE™
Shared: Space · Casual · Sandbox

SpaceBourne 2
Shared: RPG · Flight · Space Sim

Space Engineers
Shared: Space · Building · Sandbox

SpaceEngine
Shared: Casual · Space · Sandbox

My Time at Portia
Shared: RPG · Casual · Building

The Scroll of Taiwu : Beyond The Dome
Shared: RPG · Sandbox · Adventure

Garry's Mod
Shared: Building · Casual · Sandbox

Kerbal Space Program 2
Shared: Space · Building · Sandbox

EVE Online
Shared: Space · Adventure · Space Sim

Starbound
Shared: Space · Adventure · Sandbox

Stardew Valley
Shared: RPG · Building · Sandbox

Empyrion - Galactic Survival
Shared: Space · Building · Simulation

Dyson Sphere Program
Shared: Space · Building · Sandbox

Rebel Galaxy
Shared: Space · RPG · Adventure

Portal Knights
Shared: RPG · Adventure · Building

The Sims™ 3
Shared: Building · Casual · RPG

s&box
Shared: Building · Casual · Sandbox

House Flipper
Shared: Building · Casual · Simulation

Trailmakers
Shared: Space · Adventure · Flight

Rust
Shared: Building · Adventure · RPG

Between the Stars
Shared: RPG · Space · Adventure

Home Behind
Shared: RPG · Adventure · Casual