We don't usually think that you need exercise equipment in order to work out effectively. In fact, most of the time you can achieve comparable results to going to the gym simply by using your own body weight (doing push ups, for instance, or the Warrior 3 yoga pose).
But there are certain pieces of equipment that are crucial to have at home when working out. One such piece is the medicine ball, which, when incorporated into exercises, helps increase muscle intensity. Check out this video to learn how to use the medicine ball to do a twist crunch that'll tone abs and side obliques.
The main reason to work out abs is because strong abs will stabilize your lower back and prevent you from an injury; but as a side benefit a 6-pack looks great!