Lay on the ground face up with knees bent and feet on the ground. Place hands behind your head. Using your abdominal muscles pull your body up until you feel a squeeze in your abs. Then lower yourself down and repeat.
Buy a cheap jump rope at walmart or wherever you can get one. Simply swing the rope below your feet and behind your body to the front. When the rope comes around jump over it.
This most likely does not need a description but here it goes! Stand with arms at sides and feet together. Jump and spread your legs apart, while spreading legs apart bring arms over your head. When you jump back to starting position arms come back to sides.
This exercise is started in standing position. Squat down and then kick your legs back into a pushup position. Kick your legs back and then stand up. To make this exercise harder can add in a pushup at the bottom and a jump at the top.
Assume a push up position. In a fast motion bring one leg close to your stomach and back. While it is going back start to bring the other leg up. As if you are climbing up a mountain.
The iron cross is a very advanced calisthenics move. For this exercise you will need rings or TRX straps. Grab a set of rings and get into a position where your arms are fully extended and locked. Keeping them extended let the rings go out to your sides until they
Find a wall and kick into a handstand, letting your feet touch the wall. Use the wall to help you balance and lower your body up and down. This is an assisted handstand pushup and helps you build the strength to do normal ones.
Get into a handstand position and lower yourself down as far as you can go. Then push back up. Handstand push ups are a pretty advanced movement and should only be performed if you have the adequate strength.
Awesome video by Dominik Sky showing different ab exercises and progression depending on strength.