What is Codename One and how does it function? Codename One is a mobile-first solution that allows developers to create high quality cross-platform native apps. With over 40,000 developers trusting this open-source mobile toolkit, it offers a fast app development service using Java or Kotlin, with the ability to reuse 100% of the code. Additionally, the Codename One simulator allows developers to write, debug, and test apps directly within popular IDEs such as IntelliJ, Eclipse, VSCode, or NetBeans, eliminating the need to manage native SDKs. The toolkit also provides a wide variety of mobile app widgets for creating visually appealing user interfaces. Codename One offers a diverse ecosystem of both native and generic libraries/plugins that can be easily extended. Furthermore, developers can make changes to their Java/Kotlin source code that can be applied to existing apps on the go. An outstanding feature of this open-source mobile-first toolkit is that its core is free, along with the GPE + CE license. The best part of using Codename One is that apps are compiled into 100% native code, ensuring exceptional speed and performance.