  This demo paper describes a simple and practical approach to writing
cross-platform casual games using the Kotlin programming language. A key aim is
to make it much easier for researchers to demonstrate their AI playing a range
of games. Pure Kotlin code (which excludes using any Java graphics libraries)
can be transpiled to JavaScript and run in a web browser. However, writing
Kotlin code that will run without modification both in a web browser and on the
JVM is not trivial; it requires strict adherence to an appropriate methodology.
The contribution of this paper is to provide such a method including a software
design and to demonstrate this working for Tetris, played either by AI or
human.
