Non-WW Apps exist...
There are a couple of apps I have found for my iPhone.
None are WW-supported, so there is a bit of risk with that.
I have been trying iTrackBites the past week, and so far like it. It is a little herky-jerky as far as apps, and needs a little more polish, but the functionality is "basically" good. If you're not afraid to poke around a little you'll do fine. It will support either Momentum/Flex or PointsPlus. It can calculate how many points you should have with either plan to start, and as you lose. The app was 2 or 3 bucks, but I don't feel burned by the purchase. It *will* dip you below 29 PointsPlus values, which is technically non-WW approved, but personally I am ok with that. So far I'm pleased.
Previously - 2 years ago - I was using iTracker. It needs an update, as when I update my daily points in settings, my log doesn't change how many are available. Maybe they'll update it in the future, it was a great app. It was either free or a dollar, if I remember.
I am a WW lifer, and had my LO right when WW was rolling over to PP. (Just to let you know where I'm coming from.)