what is the best workout for a person with physical limitations. I use a walker?

Can't say without knowing more about the limitations. Presumably, if you use a walker, you talk to physicians now and then. Ask them.

Obviously you're not going to run marathons, but depending on your handicap, you might be able to swim or ride a bike (or both....) which is nearly as good as running.

You need a consultant with a therapist but you may be able to swim or even use a treadmill depending on your limitations and the cause but without the needed evaluations no one can safely advise you

Lift weights, use a thighmaster at waist high, bust high, shoulder high and above your head.

If you can move your legs, do leg lifts and use a thighmaster.