This is a fun experiment to check the staged rollout feature of Play Store.
There are two apks (files) published. One 'unlucky' and another 'lucky'. This second one is set to be available to only 10% of all the Play Store accounts in the world (that's what Google says, I hope it isn't lying!). Will you be one of these lucky 10%? There is only one way to know...
You can of course download the app, check if you are lucky or not, and uninstall immediately. This is an experiment, but could be fun if you are lucky and your friends aren't, for example ;)
Note: The app itself contains nothing, just a text and the icon (no ads, no extra hidden features (no easter eggs, sorry), no permissions whatsoever, and definitely no viruses or malware). For this reason the size of the apk is just a few Kb, which means that one of the screenshots on this page takes more space than the apk (I'm not joking, check it if you want).