PL/1

(I think DG always did spell it that way, not PLI or PL/I.)

DG’s PL/1 was a popular choice of language at those sites where software was developed in-house and neither (COBOL) nor (BBASIC) was deemed appropriate.

It was an optimising Subset G (General Purpose) implementation of the language with source-level debugging available via the separate [SWAT] product. There were a few features added to the subset including efficient multitasking and a very easy-to-use system call interface.

For a while (dates?) PL/1 was used internally in Data General for the development of certain system software, a role later taken over by (C).

Not to be confused with (DG/L) which was a much simpler language inspired by ALGOL and PL/1.