Group messaging applications are, quite honestly, plentiful within the Android ecosystem. When it comes to group messaging though, Google has yet to release an app which focuses on this particular aspect. Sure, Hangouts lets you chat with groups of contacts, so in a way they have a foothold in the group messaging arena, but a new app called 'Spaces' which is reportedly a non-public beta version of an app available in the Play Store suggests that Google may be looking to apply more of a focus on group messaging, and allow users to pinpoint group conversations they may want to have with other users.
According to the details that have surfaced thus far, 'Spaces' is all about topical group chats. Essentially, Spaces is no different from other group chats applications except it aims to allows users to more easily find the topics they want to discuss, all that users need to do is find things to talk about and add those topics to their "spaces," and then add people to the conversation to talk about the chosen topics at hand. Setting up the group works much in the same way as it would with other group chat apps, such as Groupme, which allows any user to set up a group chat based on anything they like (it can be given a name so other users are aware of what the group chat is targeting) and then they can add in contacts they want to have access to the group for participation.
As Spaces is a Google-based group chat app, Google search looks to be an integrated feature utilizing a Google search bar at the top of the app interface. This would likely make it simple to add content to topics or find content for a completely new group. Unfortunately, there isn't much else known about Spaces other than what can be taken from the screenshots or what's been discussed here, and this is probably due to the fact that Google is still testing the app internally. Having said that, Spaces may never actually see the light of day, but that shouldn't surprise anyone as Google often tests things that may or may not launch.