The best Simulation Games alternative to Space Engine is Reentry. It's not free, so if you're looking for a free alternative, you could try TerraGenesis. If that doesn't suit you, our users have ranked more than 25 alternatives to Space Engine and three of them are Simulation Games so hopefully you can find a suitable replacement.
Reentry is a space flight simulator based on real life spacecrafts. You create a new astronaut, gain levels and experience for every move you make by completing missions in space.
Engage in space exploration and terraform new worlds in this fun and exciting planet building simulator rooted in real science. TerraGenesis dynamically animates entire planets with changing biospheres, all based on real data from NASA.
The Tomorrow War is a space sim based on the trilogy of novels written by a famous Russian author, Alexander Zorich. These books are dedicated to the intergalactic war of two mighty empires.
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You can't terraform Jupiter, Saturn, Uranus, and Neptune.