What is the best exercise equipment for a very small apartment?

1. I have a very small bachelor apartment
2. I would like to use some kind of exercise equipment while watching TV
3. The equipment must be small and/or fold-able and hide-able
3. I can’t stand doing exercises on giant balls
4. Yoga & Pilates equipment is not of interest in this case

I would ideally like a treadmill but it has to be fold-up-able and hide-able (does this exist?). I would also consider things like a rowing machine, bike, or any other kind of repetitive machine that causes you to lose weight.