MiniComputers similar to the Molecular 18
Data General released their first system, NOVA, in 1968. This 16bit machine has a very similar instruction set to the M18, but of course, pre-dates the Molecular. Combinations of micro-instructions were permitted in the same manner as the M18, memory reference instructions were very similar although the NOVA zero page was limited to 255 words.
The technique of storing the current PC in the first location after a Jump To Subroutine was identical to the M18. In fairness, this was also the same technique used in the PDP8. I/O instructions are remarkably similar in both machines.
HP 2100 Series - again a system from a similar period and again shares a lot with the M18 and the Nova. HP 2100 Brochure