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.
AppAgg - Application Aggregator
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
Fnd - Browse Apple App Store and iTunes on the Web
APKMirror - Android Market and APK Downloads
AppRecs - AppRecs sorts through reviews in the App Store and automatically helps you filter out inauthentic results.