Cromemco - Single Board Computer
The Cromemco SBC was a self contained Z80 computer on one S-100 board.

The board had a Z80 running at 4MHz, 4K of static RAM, Cromemco's Z80 monitor in a 2716 ROM and optionally 3K of their BASIC interpreter in two other ROMs.  There were 3 independent parallel I/O ports all with handshaking. There was one RS232 serial port (a TMS 5501) with software selectable baud rates.  Finally it  had 5 independent interval timers.  Limitations were the ROM's always started at 0000H with RAM at 2000H -- hard wired.  The board however can be used with typical 64K S-100 RAM boards since the SBC simply ignores the low memory on the bus for RAM reads and writes both to the low memory on the SBC and the S-100 bus memory. The board was built for specific dedicated applications clearly.
 
The manual can be found here.