Hello,
I need to develop, as an addon to my 3D app, a messaging system, something like whatsapp, first for Android and possibly later for iOS.
I developed with Xamarin in C# (Mono for Android, not the same version used by Unity but principle is the same) the messaging part, for testing, using a service to retrieve messages when app is not in foreground and putting notifications in the top bar, etc… and now I want to port it inside my Unity app.
First of all, for my purposes it’s easier to do the 3D part in Unity and adapt the messaging app than the other way round, to write the 3D part with Xamarin, so don’t suggest that 
Which technology would you suggest to to something like whatsapp with Unity?
With Xamarin I used ServiceStack on client and server, for REST/JSON messaging over http, and it works ok.
I’ve been able to port it to Unity, and it works when the app is in foreground.
I may be interested in trying SignalR, has anyone tested it with Unity?
But most important of all: is possible to create services with Unity? I mean part of the program that continues to operate when the app is inactive (to retrieve messages)? Is there a way to achieve this?
Thanks!
Mattia