Pilates is a great way to work your body hard with low impact on your joints. The FitFormer by Pilates ProWorks is a foldable pilates machine with 4 padded foot/handle bars and 4 color-coded springs that allow for 15 increments of resistance. It has a folding frame with built-in wheels for easy transport.
This pilates machine has non-slip platforms on both ends for more exercise variety. You can find out more about it here.