http://en.spaceengine.org/

What's space engine?
An absolutely amazing space sim where you can explore the whole virgo supercluster (thousands of galaxies). Each galaxy is filled with billions-trillions of stars and each star has an average of 6 or so planets and each planet has asteroids or moons orbiting around it.

How does this work?
The game has nearly all of the known galaxies, stars, and planets in the virgo supercluster catalogued already but the rest of the stars/planets are procedurally generated.

How do I get it?
Go to the link. Download it. Its free. It is also developed by a single russian dude. He's fucking awesome.

Space Engine, the ultimate space simulator with gazillions of galaxies and planets to explore.
Download here http://www.megaupload.com/?d=BNNHCWEX

Basic Controls

Ctrl + Enter - Toggle fullscreen, better perf.
Left Mouse Button – Click to select object, Click and hold to look around
Right Mouse Button – Click and hold to rotate around selected object
Mouse Wheel – Change velocity
F1 - Options
F2 - Solar System Browser
F3 - Find-by-name menu
G - Go to an object. Press it twice to go faster.
Shift + G – Go to an object’s surface.

Shift + R - Sync your view with the object's rotation.

There are a ton of controls for the game. Simply open the ‘readme09_eng” file in the Space Engine folder to find a full list.

This game has no sound (lol space), I recommend this radio using vlc http://www.di.fm/spacemusic/

If you have trouble running the game visit this forum:
http://en.spaceengine.org/forum/4

Here are some of the possible solutions if you have crashes:

Go into the config folder and open the file “main”. Set the r_VideoMemory to what your vram is.
Try running it in XP compatibility mode.
While in-game press F4 and turn off some of the procedural options.

try set these to true (or false depends on experimenting) in main.cfg
r_BugClipping false // distant galaxies clipping
r_BugCraters true // procedural craters bug on ATI
r_BugMipmaps true // mipmap generation bug on ATI

also make sure you don’t increase some memory values too much
e.g. r_VideoMemory 950
instead of 1023/1024

if you have enough freespace and memory increase the cache values
r_gal_ModelCacheSize 300 // galaxy models cache size
r_gal_SysModelCacheSize 300 // galaxy subsystem cache size
r_cl_StarModelCacheSize 900 // star cluster subsystem cache size