beep

You can customize the number of reps and the time for work and rest.
My problem is that you only get a single sound to signal work and rest periods. This does not work for me. I want this to run this in the background while I watch something else on my mac. I count on the beeps to signal me when to work and rest. Really wish I could customise the sounds so I could discriminate the work and rest intervals without putting the app on the screen.

skipcooney about Workout Timer: tabata training