Place apples in a slow cooker. Sprinkle with sugar, cinnamon, cloves, allspice, nutmeg, and salt. Cover and cook on High for 2 hours.
Stir butter-flavored syrup, honey, maple syrup, vanilla extract, lemon juice, and molasses into the apple mixture; mash apples with a potato masher or fork.
Reduce heat to Low, cover, and continue cooking apple mixture until thickened and dark brown, 9 to 11 hours, whisking frequently. Remove cover and cook for 1 to 2 more hours.