NativeScript and React Native, as well as Xamarin and Titanium, are all trying to solve the same problem: the ability to build high-quality native applications from a single codebase. While hybrid mobile development has enabled web developers to use their skills to build cross-platform mobile apps, the look, feel, and performance of this type of an app has been lacking. Building apps that run in a WebView using hybrid mobile strategies got us halfway there, in that we have tooling such as Apache Cordova to build cross-platform using a single codebase.
Newer technologies such as NativeScript and React Native, however, are attacking the problem in a different way, avoiding using the WebView in favor of building truly mobile apps. To learn more about these differences, check out these articles: