All apps distributed through Google Play collect some device and usage data from the user. This is outlined by Google's privacy policy which is linked below.

Marijn Dillen's apps may contain advertisements by Google, Facebook, Mopub, Oath, AppLovin, and Mobfox. These third-party services may also collect data as outlined by their privacy policies which are linked below.

Google's privacy policy: https://www.google.com/intl/en/policies/privacy/
Facebook's privacy policy: https://www.facebook.com/about/privacy/
Mopub's privacy policy: https://www.mopub.com/legal/privacy/
Oath's privacy policy: https://policies.oath.com/us/en/oath/privacy/index.html
AppLovin's privacy policy: https://www.applovin.com/privacy/
Mobfox's privacy policy: https://www.mobfox.com/privacy-policy/