Amazon is really easy to upload to. I thought there was a development fee, but it's actually free. There's a simple and colorful interface that let's you put android, computer, or web apps on the Amazon market. Yesterday, I submitted my Android apps to the Amazon market so I could be more available during the holiday season. My android games were made with Unity and making them Amazon friendly was just a matter of changing the app store links in the main menus. I just hope my apps get up on time and don't get tossed back with errors. I don't have any Amazon devices to test on or money to get any so it's just wishful thinking for now.