What is the best type of exercise equipment to use with bad knees?

Zookinesis is an exercise system that combines Tai-chi, Yoga and chi-gung. It is based on the movements of animals and combines stretching, strengthening joints and muscles, improved breathing, increased range of motion of the joints and improved general health. There are versions of zookinesis that are chair exercises specifically for seniors so it will be easy on the knees.