30 Day Ab Challenge
I would give this app 5 stars and here's why...
I really enjoyed this app for many reasons. To start it has many levels based on your skill, and ability. It starts off easy and increases everyday based on level. This app also has rest days which are useful if you are busy that day and/or need a rest. Another thing I found most helpful In this app is that it sends you notifications to remind you to do your ab workout of the day.
I didn't find many bad things with this app, my only complaint was it didn't let you see what your workout would be in a few days, which can be helpful to see how much time you need to set aside.