Combine everything in a 6-quart slow cooker. Cover and cook on LOW for 8 hours.
When the cooking time is done, take a whisk and break apart the apples and nectarines, but be careful not to scratch your slow cooker while doing this.
Serve hot, or chilled.
Note- This is not a canning recipe. I used up all this sauce within a few days, If I had not used it all, I would of froze it in freezer safe jars.