fasted cardio, calisthenics, stretching... anything really

push up

strengh training

sit ups, pull ups, crunches, weight lifting, and sex.

Inter course
Hitler milking

Hindu squats are maybe the single best thing you can do without any equipment.

I enjoy doing leg blasters.

Bodyweight exercises. Isometrics. Hill sprints. Weighted hill sprints. That thing where you jump off a small thing an then launch yourself as high as possible.

All of them.

A dog can be a great fitness instructor.

If you are doing gym gear, such as a treadmill, I would suggest an iFit subscription on large screen to keep you motivated and entertained.

You could just get a bench and some adjustable weights.

Or use your own body weight with exercises, such as push-ups, etc. I would suggest something like P90x (if more advance), but you could just look up videos on Youtube and workout a plan.

Ideally you want to work out diet first and then your sleep pattern. Exercising comes after that.

I suppose there's plenty of exercises that don't require any large fitness contraptions.

squads, push ups (straight training your core.. or with knees to the side, training your sides..
leg raises.. and if you have the right equipment.. (a bar capable of holding your weight like a doorframe thats strong enoough.. pull ups and pushups..

if no weight just using to large jugs or grocery bags filled with equal weights with streched arms and holding and moving them works as well as training with dumbless..

running up and down the stairs also good exersize..

if your a millionaire. you might have a swimming pool.. swimming is the best exersize.. double the calory burn due the cold water (make sure the water of the pool is 15C or colder).. while just doing calm breaststoke.. may not feel intense but you use a lot of musclegroups so it is as effective as going to the gym.. while the cold water prevent all that nasty sweatyness and the boilancy prevents the risk of injurity..

swimming in somewhat cold water is the best possible excestize possible.

It depends on age and goals.
- I think that spine exercises are useful at any age. (so that later in ancient times we don't have to say, ah.., why didn't I do these exercises?)
- general physical exercises with dumbbells.

Pull ups.