PL/I, or Programming Language One, is a language that brings many worlds together-IBM designed it in the 1960s for scientific computation, business applications and systems programming. It was an ambitious attempt to create a "one-size-fits-all" language, and it succeeded better than you might expect. PL/I has endured decades of technological change and is still used in large mainframe environments.

What makes PL/I unique is its ability to combine the best of multiple domains: strong type control, advanced error handling, concurrency support and built-in facilities to handle both binary and decimal data. It's as if someone took the best parts of Fortran, COBOL and C and merged them into a single language. Despite its age, PL/I has been modernized-today's IBM compilers support JSON, XML and even interoperability with Java.

So while PL/I might not be the first language you learn today, it remains a heavyweight in the world of mission-critical systems. If you ever work with banking or insurance systems on an IBM Z mainframe, chances are you'll encounter PL/I-and you'll appreciate its robustness and versatility.