I use Calcy IV.
https://play.google.com/store/apps/details?id=tesmath.calcy
I used to use GoIV but the black screen loading issue, loading issues with the current version of Pokemon Go and having to restart Pokemon Go to use GoIV became a real chore to get working. If you're interested in checking it out:
https://play.google.com/store/apps/details?id=com.swanberg.pogoiv
Calcy IV works for me no problem. It doesn't have an overlay when you have to manually select appraisal information, it makes you switch out Pokemon Go into another screen to do this. It's a small but bearable hassle for me when I'm listening to podcasts or music because they pause whatever is playing upon switching back into Pokemon Go.
GoIV has an overlay for all manual inputs and the features work great, if you can get it and Pokemon Go to load.