FamiStudio is a cross platform, free and open source application for creating old school Nintendo NES / Famicom style soundtracks. We first looked at FamiStudio back in 2020 but since then there have been several new features added including support for Android devices (where it is a free download). The source code is available on GitHub under the MIT open source license, the primary language used is C#.
FamiStudio works on Mac OS, Linux and Windows in addition to the recently added Android support.
You can learn more about FamiStudio and see it in action on both desktop and Android in the video below.