We've been a fan of Kodi since it was still called XBMC. The Android version of the media centre app has been in an open beta for a while, but now that period is over. You can now download and install it on your phone, tablet or Android TV without joining a Google+ community.
The Play Store listing is still being designated by the company as a "beta", though it no longer uses Google's complex system for signing up for beta apps. There are still alpha versions of Kodi available in their Google+ community, however, if you want to try out the bleeding edge features.