Object Trails
Freeware
Object Trails
Object trails allows you to make a spline from the path of any animated object. Let's say you have a sphere traversing a spline like the green sphere below is traversing the green spline. The blue sphere is a child of the green sphere which is rotating. The combination of the blue sphere orbiting around the green sphere as it traverses it's spline causes the path of the blue moon to be as shown. All you have to do is select the object whose trail you want to convert to a spline and run Object Trails.
Choose the start and end frames which of the animation you want converted to a spline. Sample rate determines if there will be a point for every frame, every other frame, etc. A sample rate of four gives you one point for every fourth frame.