Amazon Appstore for Android
Go here and select "create free account" https://developer.amazon.com/appsandservices
The Amazon Appstore is used for publishing apps to Amazon devices as well as to supported Blackberry BB10-based devices.
Apple iTunes App Store
Go here and register for an iOS developer account https://developer.apple.com/programs/ios/
The Apple App Store is for publishing apps to iPhones and iPads.
Go here and register for an Android developer account https://play.google.com/apps/publish/signup/
The Google Play store is used for publishing apps to Google Android devices from a variety of device manufacturers, including HTC, Samsung, Motorola, LG, and others.
Go here and register for a Blackberry ID https://appworld.blackberry.com/isvportal_beta/home.do
Blackberry World is for publishing apps to supported Blackberry devices.