Formally the IPing putting app. Its amazing. Nobody at home will put it on their phone for me, and I have Android, but the pro here at work did. It is amazing... I just use the Putting part but I highly recommend it.
As for needing the cradle...NO! A little Typhoon MacGyvering here... Take a rubber shaft clamp and put it on the shaft. Put the phone against it and secure the phone to the clamp with a couple decent size rubber bands.
Learned alot about my stroke. Also was cool seeing what my loft should be on my putter, (Not the 3-4 degrees they come with). It also gives you a "putting handicap" that you want to be the same as your handicap.
Example...if you are a 10 handicap and you putting handicap is a 20, then you suck at putting... you putt like a 20 handicap. It also color codes sections so you know what is Good, ok and bad.
Of yes...in keeping with the FGI way... its FREE!