Xamarin
Mapp is currently in the process of creating a pre-built integration between Xamarin and the Mapp Mobile SDK. It is currently anticipated that the integration will be released in mid to late August 2017.
React Native
Mapp curenntly does not offer a pre-built integration between React Native and the Mapp Mobile SDK. The Mobile SDK can however be used with Reach Native with React's standard approach for integrating iOS and Android libraries.
The pertinent documentation from React Native can be found at https://facebook.github.io/react-native/docs/native-modules-ios.html