Yoga STRETCH
While this app isn’t just stretching and includes the yoga fundamentals of balance and strength the app will indeed help you become more flexible. You can customize the program to fit your needs.
Flexible Training
Not the best app on the market but frankly there aren’t super awesome stretching apps (that I’ve found yet). This one will time your stretches, gives you options for standing and sitting moves (good for those of us who work at a computer) and has good descriptions of the stretches. For $1 it’s worth a go.
Stretch Timer
If the timer built in to your phone isn’t good enough for you for your flexibility routine give this a try.