Hi,
I have three Z-80 based machines available for use via the Internet. They are a Northstar Horizon, Cromemco System One, and an Altos 5-15AD. The Altos is not S-100, but it does run CP/M, MP/M and OASIS. You can access these machines at:
http://www.imsai8080.com/computers/s100/
The...