Tabata builds cardio & endurance. I have done it with running, push-ups, and fast-punching on the heavybag.

The focus is pure speed. 20 seconds on, 10 seconds off. Or 15 on, 15 off.

Or you can do 15 push-ups every 30 seconds. If you finish the 15 push-ups fast, you get more rest till the end of those 30 seconds.