John Gruver has found a new TRS-80 Model I/III emulator called the HMP TRS-80 Emulator.
The emulator emulates a cassette-only TRS-80 Model I level 1 and level II and the Model III computer. It emulates sound thru the PC hardware and joystick via the arrow keys.
The current beta copy can be downloaded from https://www.heinpragt.com/english/software_development/trs80_emulator.html.
Thanks for letting me know, John!