http://www.techradar.com/news/android-now-lets-you-try-out-some-apps-from-the-google-play-store-before-downloading

Sick of having to download apps before you can see what they're like? Google is helping to get rid of much of that hassle by adding a "Try It Now" option beside apps on its Google Play store, which allows you to use stripped-down, web-based versions of the app rather than having to download the whole shebang. 

You'll basically be using a website, but to outward appearances it won't look or perform much differently than the app you otherwise would have downloaded.