The version of HAL that the FDA has approved is called HAL for Medical Use, and it's designed to help people with lower limb disabilities get better at walking on their own. There are other exoskeletons that help rehabilitate people through physical walking motions, but HAL is unique in the way that it relies on a mixture of voluntary control and autonomous control, using the wearer's own nervous system to signal the robot when and how to move. According to Cyberdyne, this makes the rehabilitation process more effective, because it's not just the robot moving— it's you.
Medical exoskeletons are not just science fiction. Read this excerpt from Fritz Leiber's 1968 novel A Specter is Haunting Texas, in which a man who grew up in a microgravity environment visited Earth:
This truly magnificent, romantically handsome, rather lean man was standing on two corrugated-soled titanium footplates. From the outer edge of each rose a narrow titanium T-beam that followed the line of his leg, with a joint (locked now) at the knee, up to another joint with a titanium pelvic girdle and shallow belly support. From the back of this girdle a T-spine rose to support a shoulder yoke and rib cage, all of the same metal. The rib cage was artistically slotted to save weight, so that curving strips followed the line of each of his very prominent ribs.
(Read more about Leiber's titanium exoskeleton