Isometric Wipers

How to do it

Assume a push-up position, supporting your weight on your hands and toes while keeping your body straight. Your hands should be just outside of shoulder width. This will be your starting position.
Begin by shifting your body weight as far to one side as possible, allowing the elbow on that side to flex as you lower your body.
Reverse the motion by extending the flexed arm, pushing yourself up and then dropping to the other side.
Repeat for the desired number of repetitions.

What muscles does the Isometric Wipers work?: Mainly the chest, with help from the abs, shoulders, triceps.
What equipment do I need?: Nothing but your bodyweight.
Is it good for beginners?: Yes, it is rated beginner level.
How do I track progress on it?: Log each set and beat the weight or reps from last time. Liftrung shows your last set beside the next one and estimates your one-rep max from your sets.

Exercise descriptions: free-exercise-db, public domain.