The information of this page comes from Richard Allen.
The S-PLUS was manufactured by SouthWest Technical Products who started with "kit built" computers in the back of Mechanics Illustrated. In 1982 they came out with the S-Plus system primarily for small businesses.
Utilizing Motorola's 68B09, the 2mhz version of the same chip that powered the Radio Shack Color computer, and the SS-50 bus they reached an agreement with Technical Systems Consultants of NC to provide a multi-user processing system based on a more user friendly sub-set of Unix called UniFLEX.
The 68B09 was a 8/16 bit computer. Internal process was done in 16 bits, but bus I/O was still 8 bits. Memory came in 250K boards, the bus could accommodate 4 boards, however, because of hardware I/0 address conflicts, only 750K could be accessed as RAM.
The UniFLEX operating system allocated up to 64K to each task (running program) and when operated in multi-user mode, made use of memory swapping to the HD for virtual memory.
While bus configuration allowed up to 18 serial ports, in reality, only 6-10 ports configured as multi-user was practical. If the application was CPU or I/O intensive, then that number might be reduced to 2 or 3 active users.
Early versions had dual 8" Floppy Drives 20 MB Seagate hard drives, but later versions used up to 2 40 MB ATASI drives through a Western Digital Controller. A Streaming Tape was also available.
The UniFLEX operating system was a dream, patterned after UNIX but with easier, more english language like commands emulated their Unix counterparts. commands like makdir, copy, list, find, search. Basic, Compiled Basic, Fortran 77, Cobol (patterned after Data Generals with VSAM files and a screen section).
It had a printer spooler that had features that most don't have even today.
Why did it not become popular. My option is that the primary problem was lack of trust between the hardware manufacturer and the operating system supplier. Having dealt with both sides as president of the Users Group I found both sides to be paranoid about sharing information with each other.
As a result, hardware/software development was slow, and with a lot of finger pointing. While it was marketed it as a business solution, they only developing programming and systems software, no applications.
A few attempts were made by third parties to develop a spread sheet loosely based on VisiCalc, and word processor but no organized effort was made to develop an overall office solution.