LETO
An idea I’ve had floating around for a while now is a realistic low-energy orbital simulator, that would let you move around the solar system with an ion drive. Hill Space is the gravity topography of a restricted 3-body system, and it looks a lot like terrain, which makes the movements within it intuitive… at least after you’ve seen it in action a few times.
I always imagined the story would involve a little baby AI that would have to work it’s way to the outer solar system. A few really good story ideas come to mind, but that’d be a whole other blog post.