This is something we don't hear a lot about on the list.
A lot of it is on-topic, and some of the more obscure kit was based on
fairly common single-board computers of their day. The PPG Wave ran
Flex on its Eurocom II board (powered by a 6809). The Fairlight was
based on two 6809 CPUs.
There was the old Greengate kit that plugged into Apple IIs, and an
editor for the Ensoniq Mirage that again ran on an Apple II.
I don't know what the Simmons SDX used but apparently it was a fairly
common SBC. I know the SDS7 has a 6802 on the CPU board.
Gordon.