Very simple example of sharing C# code across iOS and Android. Also includes a command-line version as a 'test harness'.
App functionality is to convert telephone number 'words' into digits (eg 1-800-FLOWERS to the actual phone number).
Deprecated versions for Windows Phone 7 and Windows 8 can be found in the GitHub repo, but require older versions of Visual Studio (earlier than 2017) to open and run.
Craig Dunn, Chris Hardy