Facebook Messenger has an unreleased feature, also called "Rooms," that allow users to create public, sharable group chats.

Also reported that each room has a link that can be shared so anyone on Messenger can join the conversation".
This new rooms feature for Messenger is said not to be as full-fledged, meaning it does offer a happy medium between the back-and-forth posting on a Group's public newsfeed and private Messenger groups, something that might be useful as the social network looks to capitalize on messaging and chatbots.