This document provides an overview of cross-platform mobile development using open source tools. It discusses hybrid mobile frameworks like Apache Cordova that allow building mobile apps with web technologies that are deployed to native app stores. While early hybrid apps had performance issues, newer frameworks discussed like React Native and NativeScript claim to generate truly native apps with high code reuse across platforms using JavaScript. The document also covers adjacent native frameworks like Xamarin that compile to native apps from C# instead of web technologies. Overall it introduces a variety of open source options for cross-platform mobile development.