Mono is a distributed effort with developers scattered around the globe, although a lot of discussion happens on the public mailing lists, some interactive discussion happen on chat.
We have several Gitter channels:
- Mono: #mono/mono
- MonoDevelop (Xamarin Studio / Visual Studio for Mac): #mono/monodevelop
- Xamarin.iOS + Xamarin.Mac: #xamarin/xamarin-macios
- Xamarin.Android: #xamarin/xamarin-android
- Xamarin.Forms: #xamarin/xamarin.forms
You can access those channels through IRC as well, check irc.gitter.im for more details.