Peel, core, and quarter the apples. To prevent browning while you are peeling, place the peeled apples in a sink or bowlful of cool water.
Place the apples, cider, cinnamon, and salt in the insert of a 5 to 7-quart slow cooker. If your slow cooker is smaller, consider making half or three-quarters of the full recipe so as not to overfill your cooker.
Cover and cook on high for 3-4 hours or on low for 6-7 hours, or until the apples are very soft.
For chunky applesauce, mash the apples with a potato masher. For a smooth consistency, puree the apples in a blender or with an immersion blender.
While the sauce is still warm, add the maple syrup. Taste and add more maple syrup to achieve your preferred level of sweetness.
Enjoy warm or chilled. Store leftovers in the refrigerator for up to one week. This recipe freezes well, too.