At CoinRoster, users can create their own contests. User generated contests can either be Public or Private, this posts describes the differences of each type. Any user can view and play public contests, but only private contests can be shared only with your personal friends and users.
Creating a public contest will allow all users to enter rosters or place a bet. Public contests are good if you want to post contest not currently offered, such as one that focuses on how many eagles a player might make in a specific round, but it doesn’t matter whether the contest is available to all users or not.
On the other hand, creating a private contest is good when you want to restrict who plays, such as when you only want to play with your friends, or when you are rewarding your own users with a private contest on special terms that is only available to users in a specific group. When you create a private contest, only users with a unique URL of the contest will be able to enter it, and private contests will not be visible on the public lobby.