Sometimes there isn't the time or inclination to go to a gym, but there is still the desire to exercise. What to do? All is not lost - there are apps that can be followed on a tablet or a phone. All you need is the aforementioned app and phone and yourself. The apps have videos with instructions on what the exercises entail. Usually you don't need anything else.
One I favour is Fitstar. There are a wide range of workouts, and you can tell it whether you found each exercise easy, just right or brutal (its word), and the forthcoming ones will be tailored to your ability. It tells you how many calories you have burnt; its estimation is fairly accurate.