There's Universe Sandbox, which while considered and marketed as a game and using some orbital calculation approaches that are outdated by modern astronomical standards, should work great for worldbuilding and simulating celestial bodies and events.
It's paid software, but it does allow you to simulate the Solar System, albeit without much accuracy very far into the future. The current version is Windows only, with the next one being made for OSX and Linux apparently. There's a free version but you can't add objects.
edit - Taemyr mentions that Universe Sandbox will not model day and night, so if you need that, you might have to look elsewhere or wing it.
edit - Having recently acquired and played Universe Sandbox, I want to add that while it's ok to use when you want to answer some abstract question ("What if Jupiter disappeared?") it really isn't very good for a realistic and detailed analysis (not to mention, it is quite buggy and not very fun). From what I gather, you really need to perform some simulations on a computational math package if you want something like that.