Fat Kingdom stores step counts, retrieved from HealthKit, locally within the app. Fat Kingdom does not store any other kind of personal data.
Steppr stores step counts, calorie counts, and distance walked, locally within the app. Steppr does not send your data anywhere. Ads in the un-tipped version are supplied via Google AdMob and use Apple's advertising identifier (IDFA),
SailCount-Pro stores data locally on your Mac and does not store anything remotely.