APK Studio - APK Studio is an open-source Integrated Development Environment that allows you to recompile and decompile Android applications with its unified interface.
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
JADX - JADX is a decompilation tool that can produce Java Source code from Dex and Apk files, being capable of providing human-readable java classes, it reverses AndroidManifest.
APKMirror - Android Market and APK Downloads
Apktool - Apktool is an all-in-one tool that can extract all the resources inside an APK.
Mobango - Mobango is an alternative Android market.