Slack

Slack screenshots

Stay in touch with your colleagues and monitor conversations.
Creating Workspace
Slack 3.1 : Creating Workspace

Alternative downloads

JBuddy Messenger
3.3
Java-based chat client. If you need to communicate with contacts on several public IM channels simultaneously and don't want to clutter your desktop.....
Rocket.Chat
2.15.3
FREE
Web Chat Server, developed in JavaScript.
GameSmith Chat
1.0
FREE
With GameSmith Chat you can quickly check out the GameSmith experience.