Gitter is a great real-time messaging service built specifically to help teams communicate better. It provides free public chat rooms for communities and open source projects and private chat rooms for teams and businesses. All of the rooms are based on Github repos, so you can easily get and use one for your favourite project.
The only downside for me was absence of native app for Windows RT, and always keeping a dedicated tab in browser and switching to it whenever you get message is not so convenient. So I did what any developer does in such situation - created one.
Fortunately, Gitter provides pretty convenient API for all the functions it provides in it's UI: http://developer.gitter.im/. Unfortunately, some parts of it are not documented, but team guys are very responsive and even fixed some pretty specific bugs in real-time, so I could continue development with almost no interruptions!
I'll probably write a bit more about complex implementation details in separate articles, but for now - you can find initial release of the app in the Store and I hope you enjoy it: