Saw this on another forum and though it was worth sharing. You can explore the Solar System, the known universe and even play around with fictional solar systems creating chaos in your own little sandbox. Great fun!
You can download a trial version (60 minute time limit) and the full version is $19.95 USD, although you can pick it up for $9.99 USD if you have a Steam account.
http://universesandbox.com/
System requirements aren't too hefty if you have an older PC:
OS: Windows 7 / Vista / XP Service Pack 3
Processor: 1.5 GHz Processor
Memory: 1 GB RAM
Hard Disk Space: 250 MB
Video Card: DirectX 9 level graphics card
Sound: DirectX 9 compatible sound card
Great fun and well worth checking out.
