TSS/8
TSS/8 is a discontinued time-sharing operating system co-written by Don Witcraft and John Everett at Digital Equipment Corporation in 1967. DEC also referred to it as Timeshared-8 and EduSystem 50.

The operating system ran on the 12-bit PDP-8 computer and was released in 1968.

Authorship

Architecture
This timesharing system:

Like IBM's CALL/OS, it implemented language variants:
 FORTRAN-D could only access 2 data files at a time, and the entire program was MAIN: no subroutines.
 BASIC-8 programs were limited to 350 lines, but "chaining" allowed "programs of virtually any length." BASIC-8 was based on Dartmouth BASIC but lacked matrix operations, implicit declaration of small arrays, strings, ON-GOTO/GOSUB, TAB, and multiline DEF FN statements.
 PAL-D (Program Assembly Language/Disk) allowed the "full standard" but, like all TSS/8 programs, was restricted to 4K.
 ALGOL was implemented as a known standard subset, "IFIP Subset ALGOL 60."

It also supported DEC's FOCAL, which was "developed specifically for the PDP 8/E" and it provided "an algebraic language" and also a "desk calculator mode."

Historical notes
 TSS/8 sold more than 100 copies.
 Operating costs were about 1/20 of TSS/360.  TSS/8 was also designed to be more cost-effective than the PDP-10 "for jobs with low computational requirements (like editing)".
 The RSTS-11 operating system is a descendant of TSS/8.

References

DEC operating systems
Time-sharing operating systems
1968 software