Included with the recent update to Royal Caribbean's app is the option for guests to initiate group chats while on their cruise.
In addition to the one-to-one guest chat feature that is being tested on Harmony of the Seas and Allure of the Seas, the 1.16.0 version of the app comes with a group chat feature.
Thanks to Jody Finds The Travel Deals for providing the screenshots.
The chat feature is currently only available on Harmony of the Seas and Allure of the Seas while it is being developed and tested. Eventually, all Royal Caribbean ships will have access to the app, along with chat, however there is no timetable provided for when each ship and/or feature will be released.
There is no cost to use Royal Caribbean's app while onboard and you do not need an internet package to use the app either.