Exercise Ideas

My treadmill quit. I have a small stepper but it is hard on my knees. I have had 3 knee surgeries and arthritis is setting in. Any suggestions on alternative do at home exercises. I don't have access to a gym which is what I prefer for weights but I have to get my exercise level up. I know I can do outdoor walking. I live on a gravel road and don't want to develop rickets (? not sure that is the right word).