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Google Play (formerly the Android Market) is an online store by Google for Android devices. Browse and search for apps, books, and movie rentals from your web browser or Android device.

Cydia is app store and package manager that lets you download apps that haven't been approved by Apple for your jailbroken iPhone, iPad and iPod Touch.

The App Store lets you discover hundreds of thousands of applications that you can download for your iOS device. Browse the App Store for games and apps for business, entertainment, and more.

In an effort to make things easy, and maybe even fun, AndroidPolice.com created APK Mirror. Over the past several months, they've been working to build a smooth, reliable, trust-worthy site to host the downloads users love.

Download apk directly from Android market even without Google play store account, APK Pure is a totally free APK downloader for Android phone and tablet

Mevvy is an app discovery platform that follows a different concept - we categorize apps by interest group, and help you discover the apps that truly matter to you - whether you are a parent, a pilot, a marketing strategist or an athlete!

The Amazon Appstore is a place to purchase and download apps for your Android device. You can get a paid app for free every day, and see app recommendations based on your past Amazon purchases. You can also test apps on a simulated Android phone using a feature called “Test Drive.” Access the Appstore from your computer's web browser, or directly from your phone or tablet.

Discovering new applications

Discover and play paid apps and games for free.

AppCake (by iPhoneCake.com) is an active community where people share their IPA and APK files, so you can download and install them on your device.

A powerful tool for finding new apps. Search and filter, see recommendations, and see ratings based on just the most trustworthy customer reviews.

iNoJB, formerly known as "iNoCydia", is a Cydia alternative made by Colton, It has many tweaks as well as apps from the Emu4iOS Store that require no Jailbreak or PC to install. As of version 2.0 it has a developer panel, user-uploaded apps, a native app, and optional in-store purchases. It is one of the best stores out there and I would go get it right away!

SAM - SlideME Market Application Manager is a commercial software client (see http://slideme.org/eula for End User License Agreement) for your mobile device. Simply use SAM to install applications wirelessly 'over-the-air', without any further need to download to your PC applications and run install scripts to load your application to your device.