Anyone who knows me knows that I am a bargain shopper. I like to claim that I'm a "frugalista." :o) Therefore, the apps that I discuss on here will either be free (like this one) or inexpensive and worth the money.
"Speech To Go" is an app that I found that targets articulation. It includes every phoneme (sound) in the English language. Each sound has a name (hard c, like k), a voice will make the appropriate sound with examples of words that begin with that sound, then it gives an explanation of how that sound is made. It is a neat tool for therapists if you are having a hard time explain what your articulators (tongue, teeth, palate, etc) are doing when making the sound. I wish it had a video example as well, but I guess you could always show your client too. It can be helpful for parents to know how to explain to a child what should be happening. Plus, the kids are hearing another good example of that sound. This is another time that a visual might come in handy, but that's not included in the app.
It's not a "must have", but it can be handy.