Tired of buying an app only to find it's not at all what your looking for, well Amazon has you covered with their "Test Drive" feature which enables an emulator on your computer screen for navigation through the application as you would see it on your device
Here's how it works
Clicking the “Test drive now” button launches a copy of this app on Amazon Elastic Compute Cloud (EC2), a web service that provides on-demand compute capacity in the cloud for developers. When you click on the simulated phone using your mouse, we send those inputs over the Internet to the app running on Amazon EC2 — just like your mobile device would send a finger tap to the app. Our servers then send the video and audio output from the app back to your computer. All this happens in real time, allowing you to explore the features of the app as if it were running on your mobile device.
See it in action via Amazon