Yahoo just listed its own group chat app on Google Play. The app, Squirrel, is invite only as of yet, and brings a mixture of messaging app and team chat functionality.
You can create chat rooms - both public and private - share files and photos with people in those rooms but also mention people to get their attention and send Blast messages which are more important and are seen by everyone - like in popular team chat app Slack.
It's interesting to see what the new Verizon-owned Yahoo will do now. But if this is any indication, Yahoo is getting more serious about messaging.