This document discusses building real-time cross-platform apps with SignalR and Xamarin. It describes Xamarin as allowing development of native Android, iOS, and Windows apps using C# and sharing code. SignalR is introduced as simplifying adding real-time functionality by allowing server code to push content instantly to clients. The document notes that the SignalR .NET client works for Xamarin apps as well as JavaScript, allowing cross-platform real-time apps to be created using these technologies.