SD Systems made a name for itself designing and selling S-100 boards. The most popular was their line of ExpandoRAM dynamic RAM boards. They also sold a few Z-80 CPU boards, the VersaFloppy I and II floppy disk controllers, an 80x24 video board, along with a few other boards. Manuals for most of their board products are available in the Resources section at the bottom of this page.
SD Systems also sold a few computer systems, though the sale of computer systems appears to very limited.
One of the computers sold by SD Systems was the SDS-100 Computer. It provided a 4mhz Z-80 processor, 80x24 video, and two 1mb DSDD 8" floppy drives as can be seen in this ad.
The pictures below are of an SD Systems 51009 computer I restored. This computer appears to be a custom product developed by SD Systems for TBS International, a shipping company. The capabilities of this system are very similar to the SDS-100 computer above.