Im currently working on a highly optimised PC Engine emulator for RISC OS. Sound is fully emulated and on a StrongARM the speed is typically well in excess of the magic 60 fps, so its possible a multitasking version may appear later on. It is still very much a work in progress, but you can download an early version here now version 0.21. The source code is also available, although its pretty messy in places and in dire need of an overhaul. Download it here if you dare : If you downloaded the pce021.zip or pce021src.zip file before August 26, you might want to download this tiny patch. Id forgotten to reserve a big enough chunk of memory in the Run file for large games like BomberMan 94, resulting in a rather horrible crash when you ran them. Just copy the PCEngine in the patch archive over your current PCEngine application and all should be fine.

Website: http://www.plasma.demon.co.uk/pcengine/pce.html