I've recently become a huge fan of Space Engine, a space simulation where you can explore the universe. (See link below)
The main appeal for me is visuals, but it has its' limitations. While you can create systems, it's a rather difficult process. I use Universe Sandbox for setting up the systems, and plug in the data via editing notepad++ documents for SE. What would be a cool update, if it's possible, is if we could save systems in a format that could be easily transferred to SE.