This is a free and fast 1 to 1 video call app from DT Mobile, where 2 users can connect without registrations and wasting of time. Just input one key phrase (channel name) on 2 sides and click "Join".
Its free opensource project written on Xamarin with Agora SDK.
You can find source code of the app here: https://github.com/DreamTeamMobile/Xamarin.Agora.Samples