NativeScript is how you write truly native cross-platform mobile applications with JavaScript, TypeScript or Angular. You can always directly access all native platform APIs on both iOS and Android from JavaScript, TypeScript or Angular. NativeScript works differently than Cordova, PhoneGap, Ionic, Xamarin and React Native.
If you are in technical management, we've put together the CTO's Guide to NativeScript. If you are more comfortable with development, head on over to the NativeScript Playground and try NativeScript in 5 minutes.