Algodoo

This scene has the sun, inner planets and their moons. All masses, sizes, distances and orbital movements are in realistic scale in relation to each other.

All movement happens due to gravitational forces between celestial bodies (except Mars' moons which are linked to Mars because they are just too small).

Planets' rotation speeds are realistic but their angular positions or orbit inclinations are not taken into account (that would of course require 3d space).