Sensor Tower - Sensor Tower is a platform for app store optimization and app industry intelligence.
F-Droid - F-Droid is an interesting alternative for Android users who want to try something different and not have to use the Goole Play store all the time.
App Annie - App Annie is a marketing analytics tool available for apps of all kinds. With App Annie, you can track sales, traffic, and a variety of other factors pertinent to monitoring an app's trajectory.
APK Pure - Download apk for Android with APKPure APK downloader. NoAds, Faster apk downloads and apk file update speed. Best of all, it's free
appfigures - Cross-platform app store analytics for all of your mobile apps.
APKMirror - Android Market and APK Downloads