I like this one for $4.99:
https://itunes.apple.com/us/app/wnb-...408836204?mt=8
because it allows for some pre-set weights at certain stations. For example, I don't have to remember how much my rear seats weigh - I can just move the "rear seats" slider to the right when they're installed, and to the left when they're not. I also carry some odd but specific cargo occasionally and it lets me add or subtract it with a finger swipe, and I don't have to remember how much it weighs or its station.
I use it to send emails of W&B for PALS (similar to Angel Flight) preflight.