It's a procedurally generated universe simulator that's based on actual science. Space engine can generate some incredible sights, from alien planets with great landscape to black holes colliding, you will find everything here.
You can travel the cosmos at 300 light years per second and there is "virtually" no limit to how much you can explore.
It even has inbuilt search tools that can find planets that support single celled or even complex life.
You can also fall into a gas giant.

Also has great ambient music from some underrated artists. A must play for anyone that likes space.