BPCS stands for Business Planning and Control System.
BPCS Programming languages
Some BPCS sites use IBM Tools that might not strictly be considered programming languages such as PDM Query DFU SDA REXX.
Some BPCS sites may be on ancient versions of BPCS associated with OS that came before OS/400 such as the SSP of S/36 and the programming languages supported there.
We need to be careful with CLP/400 examples not to include any code that came with BPCS since that is copyrighted and licensed.
BPCS Hosts & Versions
BPCS is available and is used in many flavors.
Most companies run it on AS/400 or iSeries as opposed to the alternatives: some UNIX host; Oracle; or Windows.
The Windows hosting only works when whole company has a very small number of seats, and this should not be confused with people using Windows as the GUI means of Client Access to their BPCS data.
Most popular versions appear to be V6 variants then V405CD but this is a moving target.