Muscles worked: abs, obliques, quads, hamstrings, deltoids, biceps, triceps, and the chest.
Start off in the standard push up position. Pull your knees up to your chest, one at a time, in quick succession. You want to keep your body in a push-up position all the way through the exerc...

Muscles worked: quads, glutes, calves, hamstring, core, inner thighs.
As you are standing straight, take a big step forward and bend your knee so your rear knee almost touches the floor. Then kick yourself back up with your front leg and return to your original position. Do the same ...

Muscles worked: hamstrings, chest, triceps.
Start by standing up, legs a little bit less than shoulder-width apart. Bend over like you wanted to touch your toes, but instead, place your palms on the floor and walk forward with your arms until you reach the standard push up position. ...

Calisthenics is a form of fitness consisting of different movements that exercise large muscle groups: running, standing, grasping, pushing, etc.
You don't rely on anything but a person's own body weight.

Muscle areas activated: all your back muscles, biceps, forearms, core.
You need is a surface you can hang from with your legs extended in front of you. Start by hanging onto the bar, heels on the floor, your back and legs straight, core engaged. Pull your body closer to ...