Here are some unique, or not so unique, exercises that I have picked up over the past few months. They are meant for strengthening your core, legs, arms, and more, and they can be done whenever/wherever you please!
Bent Knee Heel Touches: Lay with your back on the ground, and lift your knees so that you make a 90 degree angle between your thighs, knees, and heels. Now bring your heels down to the ground, and back up! It may help to put your hands underneath your butt.
Russian twists: Sit up so that you are making a square root symbol (back and thighs are the V part and your shins are the line). Now take both of your hands, look at them, and twist so that you touch the ground by one of your sides. Now twist to the other side.
Burpees: Now this is a fun exercise–just kidding. Here we go. Stand up straight. Next reach your hands to the ceiling and while you are doing this, jump up. Land so that you are crouching down, put your hands down, and push your legs out by doing something similar to a  hop. It’s hard to explain, but in any case, both of your legs should “take off” and land at the same time, not one after the other, and you should end up in a push-up position. Do a push-up, use your legs and jump them right back underneath you, and jump up to touch the ceiling once again.
Rotational Push-ups: This exercise is very similar to a push-up. Instead, of bringing your body straight down and up with your arms, try to get one side of your body to touch the ground. Now come back up, and bring the other side down. You’ll find yourself bending one arm further down than the other, straightening up, and then bending the other arm down further.
Good luck!