On: Basecamp 3 for iOS: Hybrid Architecture

[WA]

Can you also share between iOS/Android and Web with Xamarin? Because that's what Basecamp's approach helps with.

[yAak → WA]

Not in terms of UI, no. If you write your non-UI code in shared libraries that are PCL or .NET Standard and have your web-server use them too, Xamarin enables that scenario, but doesn't really bring anything else to the table for a web app.