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
Aurora Droid - An alternative to the default F-Droid app with an intuitive UI and multiple features.
APKMirror - Android Market and APK Downloads
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.
Uptodown - Uptodown is a mobile app and website that lets you download games and apps to users on most of the major platforms.
Aurora Store - Aurora is a FOSS Play Store client that does not require a Google Account to download directly from Play Store. However you can login with your Google Account to download your already paid apps!