AppAddict - AppAddict is an online tool that allows you to download third-party apps on your devices without rooting or jailbreaking your devices.
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.
25pp - 25pp is App Store that contains exclusive apps that are not yet available on app stores.
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
Kuaiyong - Kuaiyong brings features to install free as well as paid apps on Apple devices without jailbreaking them.
APKMirror - Android Market and APK Downloads