Y'know, the Prison Workout really produces results.
It's burpees done every day in descending sets.

You're supposed to build yourself up to starting at 20 reps and working your way down to 1.
1st set 20 reps , 2nd set 19 reps, 3rd set 18 reps, and so on, till 20th set 1 rep.
210 reps total in one workout is your goal.

It'll kick your @$$..

I did it for 30 days every day without fail about two years ago just as an experiment.
Didn't change my diet nor do any other form of exercise.
Started at 8 reps I think. Gradually built up. I was in good condition at the end of 30 days.

There's different types of burpees. I did the kind with the jump, exactly like this woman does them:



It's very monotonous, so it's not something I would stick with.
It does what it's designed for: works your muscular and cardiovascular systems with no equipment in an enclosed space. Develops bursts of energy, speed, power, and endurance, full body workout, and develops quicker recovery of wind between sets.

Try dropping to the floor right now and do 10 fast ones the way the chick in the video does them, you'll feel it, your cardio will feel it.

Working out though, you need something you kind of enjoy doing or don't mind doing, so it becomes part of your healthy lifestyle. Burpees was something I dreaded, but it was an experiment, and it definitely produces results.