Place the cranberries in a food processor. Process until coarsely chopped. Transfer the cranberries to a large bowl, and stir in the pineapple, apple, celery, and sugar. Combine the gelatin and boiling water in a separate bowl, stirring until gelatin dissolves. Pour gelatin mixture into the pineapple mixture; stir to combine. Cover and refrigerate until gelatin sets, about 2 hours.