Cydia - An alternative app store for jailbroken 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.
Zestia - Zestia is a mobile app designed to assist you in organizing your hectic schedule, social life, and professional persona.
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
JazzMyApp - Let JazzMyApp surprise you with amazing apps everyday. Try it out yourself.
APKMirror - Android Market and APK Downloads