First of all, you want to get your hands on something like this:
Ball 100% Natural® Fruit Jell® No Sugar Needed Pectin (51200)
Secondly, you'll want some form of artificial sweetener. Splenda works well. If you want the cleanest sweetness possible (no aftertaste), you'll combine the splenda with another sweetener like a sugar alcohol or acesulfame K. Nutrasweet won't work as it will break down with heat.
Third, you'll want an alternative bulking agent that will provide the textural effects of sugar. Sugar alcohols are popular but can cause digestive problems if consumed in excess. Polydextrose is a popular additive in commercial sugar free jams. I bake with polydextrose and have found it to be an exact replica for the texture of sugar.
If you want to avoid the actual sugar from the fruit (ultra low carb), then it get's a little trickier. You can either choose low sugar fruits like berries or you'll need to start looking at natural flavorings as a way of supplementing the fruit flavor without additional sugar. I have a few links for those if you're interested.
This is all based upon the best sugar free jam possible. If you want something that involves less effort but still gives you something edible, gelatin and splenda will work.
Apple sauce, corn syrup, apple juice - all high in sugar.