Orbiter is described as 'Realistic 3D real-time space flight simulator program' and is an game in the games category. There are more than 10 games similar to Orbiter for a variety of platforms, including Windows, Steam, Linux, Mac and Android apps. The best Orbiter alternative is Space Engine. It's not free, so if you're looking for a free alternative, you could try Zen Koi or Pioneer. Other Orbiter like games are Children of a Dead Earth, Universe Sandbox, Spore and Elite: Dangerous.
Space Engine - a real-time 3D space simulator, procedural universe generator and visualiser. It lets you explore the universe in three dimensions, starting from planet Earth to the most distant galaxies.
Children of a Dead Earth is a simulation of true-to-life space warfare. Design your spacecrafts using real world technologies. Traverse the solar system using actual orbit mechanics. Command fleets as the solar system descends into war, and see if you have what it takes to...
Create & destroy on an unimaginable scale with a realistic physics-based space simulator. Explore the beauty of our universe and the fragility of our planet. Use science to bend the laws of gravity, collide planets, boil away oceans, fire epic space lasers, and customize your universe.
Zen Koi is a fun, relaxing and stylish mobile game experience from LandShark Games. Grow, breed and collect beautiful Japanese carp as they make their way to mythological dragon form.
Spore is a multi-genre single-player god game developed by Maxis and designed by Will Wright.
Spore is more akin to Minecraft as game of creative play, whereas Orbiter is a "game" for simulating the space-flight experience.
Elite: Dangerous is a space adventure, trading, and combat simulator that is the fourth release in the Elite video game series.
Create and manage your own space program, build and fly spacecraft, and try to conquer space.
KSP, while cool in itself, is not that much like Orbiter. The two shares the space-thing setting, but similarities kinda end there. Orbiter is a full-blown simulator, while KSP provides more of a casual (good!) experience for those who likes space, spaceships, etc (KSP also lets you create and improve along the way your spaceship)
Pioneer is a space adventure game set in the Milky Way galaxy at the turn of the 31st century. The game is open-ended, and you are free to explore the millions of star systems in the game. You can land on planets, slingshot past gas giants, and burn yourself to a crisp flying...
A game of missions, trade and space combat in the 31st century using the Pioneer Space Sim engine with many additions and improvements.
Set up a Portal in your real-life room, and seamlessly step into any spatial worlds you create with AI.
Systems Tool Kit (STK) is a platform for analyzing and visualizing complex systems in the context of your mission. Interact with data from platforms across the aerospace, defense, telecommunications, and other industries.
Space Simulator is a realistic space flight simulator for iOS and Android. It is an open-ended simulation where players can free roam Solar System or reenact historical NASA space program missions.
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Orbiter is a spaceflight simulator that has a 1:1 replica of the Solar System and utilises realistic spaceflight physics, while Spore is more of a casual game that focus on the evolution of your species from its origin (where spaceflight is only a small part of it), set in a procedural galaxy with cartoony graphics.