Place cranberries in a food processor; process 30 seconds or until chopped. Combine cranberries and sweetener in a large bowl; let stand 30 minutes or until sweetener dissolves. Combine gelatin and boiling water in a large bowl; stir 2 minutes or until gelatin dissolves. Chill until the consistency of unbeaten egg white.

Stir cranberry mixture, celery, and apple into gelatin mixture. Pour mixture into a 3-cup mold coated with cooking spray. Cover and chill until firm.

To serve, unmold salad onto a lettuce-lined serving plate, if desired.