Nights Keeper was removed from Google Play. Official reason is Violation of the Permissions policy. The talk is about access to SMS which is really required for my app and now restricted by Google policy.
I’m trying to solve this problem. Will update results here.
Last version (with permissions changes and new API support) can be downloaded by following link: NightsKeeper_v2.8.0.apk.
Last officaly published version from Google Play can be downloaded by following link: NightsKeeper_v2.7.8.apk.
Please, don’t download it from other sites, it can be infected.