Codes pw2bgw.x and bgw2pw.x convert data files from pw.x to a format suitable for usage by the Berkeley GW code, and vice versa. See files Doc/INPUT_pw2bgw.* and Doc/INPUT_bgw2pw.* for input data documentation.
Undocumented code pw2gw.x converts data files from pw.x to a format suitable for usage by another GW code.
Code pw_export.x, not compiled by default, is an interface to other codes, documented in Doc/INPUT_pw_export.* Code qexml.x, not compiled by default, is a template that is useful to follow when wrting interfaces.