I need a free open source planetary orbit simulator software that should be able to calculate orbit stability for a couple simple planetary systems. Basically, I need to calculate orbit durations for a simple system I am building as a background for a fantasy story (so there won't be science fiction involved, I just need that to have some sort of possible year duration and such. In this stellar system, my planet is a moon orbiting a Jupiter-like planet, and it is tidally locked. The Jupiter like planet orbits its star, so the moon/satellite also gets some sort of day/night on both sides from the star. Besides, that star also orbits a binary system.
So, is there any good free open source planetary orbit simulation software that would enable me to simulate this whole system with the star that orbits the binary system, the Jupiter-like giant that orbits that star and the large moon that orbits the giant planet?