Google is rolling out a Try Now button to test instant apps on the Android Play Store
You do have to be running a fairly recent Android OS: Android 5.0 (API level 21) through Android 8.0 (API level 26). Support for the feature also needs to be enabled from the Google settings interface on the device. Lastly, there might be some market limitations or a staged roll-out in place, so, if you only see the familiar old "Install" button after going through all the steps, you should try a different device or wait a bit, since this is only the beginning.
Google is experimenting with a much more flexible design model, where a user would only be presented with parts of an app that are relevant to his current activity.
This will be a great way to test out compatibility features of n app without having to go through a whole download and uninstall. It also removes the need for a separate demo app in the Store.