In a medium saucepan, bring sugar, water, cinnamon, and salt to a boil over medium heat. Stir occasionally until sugar is dissolved.
Stir in cranberries and apples. Simmer until slightly thickened and the berries begin to pop, about 10 minutes.
Remove from heat and cool to room temperature, about 1 hour.
If you're using frozen cranberries, just add about 2 minutes to simmering time (no need to thaw).Make it ahead! Just follow the recipe as is, cool it completely, and then keep refrigerated for up to 4 days in advance. Or, freeze it a month ahead and just thaw in the refrigerator overnight before you want to serve it. Easy!