PDP-11 and VAX compatible systems, only with more modern components in a unit that you can fit in a rack rather than a whole room.
These systems are really aimed at military and government customers who can't migrate mission critical systems (often literally mission critical) to other platforms. You can assume that these boxes are probably not cheap.
Of course, you'll probably want a terminal to go with it.. and the old DEC VT520 (now made by Boundless Technologies) is still available for a fairly hefty $550 a pop.
You can do it in software too with an emulator called CHARON which has a free version for noncommercial use. You can't stick your ancient Qbus cards on that though.
Now, if this Multics emulator ever gets made then that would be super awesome.