I prefer ITS DDT (aka HACTRN), with its built-in PDP-10 assembler and disassembler, that lets you do things like your login file customizing your prompt in assembly code to print the time by making system calls, without actually spawning any sub-jobs to merely print the time:

https://gunkies.org/wiki/ITS_DDT_Guide

  ..PROMPT
      holds the instruction which DDT uses to type out a "*".
      You can replace it with any other instruction.
      To use "%" instead of "*", deposit $1#%$> in that location
      ($> to avoid clobbering the opcode without having 
      to know what it is)

If you have to use arcane syntax and grawlix profanity, you should at least have direct efficient access to the full power of the CPU and operating system.

https://en.wikipedia.org/wiki/Incompatible_Timesharing_Syste...

https://en.wikipedia.org/wiki/Dynamic_debugging_technique

https://web.archive.org/web/20061011004003/http://www.sigfs....

https://its.victor.se/wiki/luser

https://www.hactrn.net/sra/alice/alices.pdp10

https://gunkies.org/wiki/Incompatible_Timesharing_System

(I recognize that photo I took of MIT-MC at the MIT-AI Lab!)

https://gunkies.org/wiki/File:Mit-mc.jpg

Even the Apple ][ Integer Basic monitor ROMs had a build-in mini assembler and disassembler.

https://www.ldx.ca/notes/apple2-notes.html