Ninite - Ninite is the easiest way to install software.
Aptoide - Aptoide is a third party replacement for the traditional Google Play Store.
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
Amazon Appstore - The Amazon Appstore is a place to purchase and download apps for your Android device.
GetJar - Discover and play paid apps and games for free.
APKMirror - Android Market and APK Downloads