Worth grabbing if you can get it while it's free for any infant-age range children.
www.facebook.com/TeachYourMonsterToRead/ has the links to all the different app stores on it - Apple/Google/Amazon Fire
Hopefully not marked as marketing spam MNHQ - it's just an app that's mentioned very regularly and normally costs a bit of cash.
(If you miss it - follow their social media and it comes up for free periodically)