If you are familiar with things like Slack or Discord it is something like that. It is based on Mattermost which is a very nice open source platform for chats via computers or phones. You can join 'rooms' which revolve around certain topics or interests.
You can also talk privately with people, though I am not wholly sure if it is encrypted chat or not. Methinks probably not. Still there are other solutions for that which you can ask me about if you are interested.
Hope that helps.