Seiko: Where fools rush in - we made sure...

Perhaps more famous for its digital watches, Seiko had its own Business Computers line and launched this - the Series 8600 - in 1983.

It ran on an 5MHz Intel 8086 CPU and came with the option of at least five operatings systems - CP/M-86, MP/M-86, MS-DOS, OASIS16 and UNIDOL[source: https://www.1000bit.it/scheda.asp?id=787].

The availability of MP/M-86, together with its design, meant that the 8600 could support up to four additional users via additional terminals, using serial RS232 links, making it a small multi-user system at a time when this was still seen as a thing. 

The widespread availability of networking and the commoditisation of PCs would eventually make multiuser systems redundant in most situations.