Rinse the cranberries and discard any stems or damaged berries.
Add the cranberries and water to a sauce pan. Bring to a boil over medium-high heat.
Reduce the heat to medium and let the mixture continue to boil, stirring often.
The berries will start to pop open and foam up. Let them boil for about another 15 minutes. You want the liquid to reduce by about 1/4 and thicken to the point that it coats the back of a spoon. When it reaches this point, remove it from the heat.
Place a fine mesh strainer over a large bowl. Pour the cranberry mixture into the strainer. Strain until all the juice and jelly has come through. Press down on the berries in the strainer with a spatula or wooden spoon to extract as much jelly as possible. Check the bottom of the strainer for any jelly that clings and scrape it off into the bowl.
Return the strained jelly to the sauce pan. Bring back to a low boil and add the sweetener. Stir until just dissolved, about 30 seconds. Immediately remove the pan from the heat.
Stir in the orange extract, if desired.
In a small measuring cup, mix the gelatin and water. Add the mixture to the jelly and whisk until it's fully dissolved.
Transfer the jelly to clean metal cans, wide-mouth mason jars, or small dessert molds.
Let the jelly cool to room temperature on the counter or a wire rack, which will take around 30-45 minutes. Then refrigerate it for at least 6 hours, up to over night.
When you're ready to serve, slide a small rubber spatula or butter knife around the inside of the container to loosen the jelly. Invert onto a serving platter and slice as desired.