Since MULTICS had a high quality PL/I compiler, you can install the emulator to play with the language. The "shell" is different from Unix but shares some similarities.
About 3/4 of the way down this page, is the PL/I source code: https://multicians.org/pl1.html
Simply because some of the source file (1 or 2) for CPM are written in PL/1, rather than the majority having been written in PL/M, then eventually translated to assembler.
Here we go:
http://www.cpm.z80.de/binary.html
PLI-80 BINARY : 146K This is the PLI compiler. It is very compatible with the IBM PLI compiler used on the 360. The only functions I found missing were DATE and TIME, which were easy to fake out. (Apparently this is version 1.0).
PLI-80 version 1.3 : 111K Here is the PLI-80 version 1.3 compiler and libraries.
PL/I-80 version 1.4: 188K - version 1.4 including quite a few example files