Midpoint was created to test dynamic map creation based on user latitude and longitude coordinates. In order to use the feature, you will need to have an account with Google Play Services. You probably have one already if you're downloading from this page.
Midpoint includes on-screen helper animations with info text to help you get started. In order to add a player, you will need for that player to be in your Plus Circles. If they are not in-game at that time, Google Play Services will send them a notification where they can automatically join the room. Room joining is automatic and you are given the option to leave any room at any time.
No public information is shown. Neither users nor yourself can see your current location information.
NOTE ABOUT PERMISSIONS: Yup, there are a LOT of permissions enabled. These are always enabled inside of games that are used for testing purposes. Any information obtained (in this case only your location info is obtained) is never and never will be shared.
Midpoint was created for the sole purpose of testing features for another game that's named, you guessed it, Midpoint: The Game.
Obviously, in order to create a robust web presence, we need content. That means we'll need to make more games and junk that people can play around with, so currently, there will not be a site for public access, however, it's not far off!