TalkFit lets you design a sequence of steps that will be read out while you exercise, so you dont need to look at the screen once it has started. Its ideal for timed workouts like stretching or cardio exercises!
TalkFit works with music, and works when your phone is locked, so you can just start a routine and let it run. It will dip the volume of your music while instructions are playing, and you can choose to have it play tones periodically during your exercise to keep you informed of your progress. You can also choose to have a countdown let you know the end of a step is coming!
The voice used by TalkFit is completely configurable: you can choose the language and country as well as adjust the pitch and speed of the voice.
You can try out TalkFit for free (its limited to 3 routines by default) and if you like it you can choose your own payment amount to unlock unlimited routines.