App Store Clients & Downloaders (Mobile Apps): open-source projects that exist because someone reverse engineered a closed product, sorted by GitHub stars.
CLI that searches and downloads App Store IPAs using Apple's private store APIs
Android app that downloads APKs directly from Google Play
iOS app to download and install App Store IPAs, inspired by ipatool
Unofficial Google Play Python API
Raccoon: desktop APK downloader for Google Play
Python ipatool for downloading IPAs from the App Store
Command-line Google Play APK downloader
macOS app to download, re-sign and sideload App Store apps
GUI for ipatool on iOS
Google Play desktop client (legacy Raccoon)
Chrome extension that downloads APKs from Google Play
Downloads APK files directly from the Google Play Store
JavaScript implementation of ipatool
PHP implementation of the Android Market API
Script to purchase and download App Store apps, including removed ones
Unofficial Google Play Store API
APK downloader for several stores
On-device iOS command-line ipatool
Downloads apps from APKMirror
Ruby client for the reverse-engineered Android Market (Google Play) API
Swift library and CLI reimplementation of ipatool
Downloads APKs from the Samsung Galaxy Store
APK downloader for apkpure.com
Fetches iOS app data from the App Store through undocumented internal iTunes APIs
Unofficial Python library and CLI for public Google Play Store search and app details
Open-source Google Play client using the reverse-engineered Play protocol
Downloader for apps from the QooApp store