Tabata Stopwatch Pro is an app I use whenever I do a tabata workout at home. I like that you can personalize it. Tabata is one of my favorite workouts and this is a lifesaver for doing it at home!
Interval Timer is an app I use for running/walking and other timed workouts. I have been using this app for training to run a 5k. I needed to build myself up slowly as far as running times and this helped me when I was running outside to let me know when it was time to run or walk. I also use this for a workout my trainer has me do where I do 10 exercises back-to-back for 60 seconds, 30 seconds, and 15 seconds with a rest between each set. It sounds easy, but it's killer!
I used Sworkit Pro a lot before we got a treadmill for cardio days. I am now doing run/walks on cardio days, but I still love to use this app when I am traveling. It lets you choose what type of workout you would like to do (cardio, strength, yoga, stretching) and then you can continue to customize it for a specific amount of time.