What is the most popular piece of Pilates equipment?

The most popular piece of Pilates equipment is the Pilates reformer. The reformer is a machine that consists of a sliding carriage that's attached to a set of springs and pulleys. The user lies, sits, or stands on the carriage and performs exercises that use resistance from the springs and pulleys to target specific muscle groups. The reformer is a versatile piece of equipment that can be used for a wide variety of exercises, making it a popular choice for Pilates practitioners of all levels.