Space engine in one scentence: Discover the entire universe (and beyond).
This game engine simulates the entire universe and you can fly around it. this means discovering everything that we know there is in the universe.
I think this is the ultimate simulator in the universe (pun intended).
If you think this is impossible; look for yourself on: Space Engine - Home page and you wil be blown away.
This is a picture of one of the BILLIONS of galaxys
each dot is a solarsystem with planets.
and you can go down until you get this view

there is only a loading screen when you enter a planet.

please i also must urge everyone to donate together to the crazy Russian who made this possible: Vladimir Romanyuk
if all the bro's got donate even 1 dollar/euro (or even yen for that matter) Pewdiepie could explore the universe with us.