It's old tool to convert polish diacritical chars in text files. In old days we had over 30 so-called standards :) We love you UTF-8 ;)

You can compile the source yourself, but I guess classic Borland Pascal is required. Here's the main source:
 plc.pas 21.1K
required modules:
 incmisc.pas 18.5K
 incdisk.pas 12.7K
 altcrt.pas 5.0K
documentation (also printed below), those weird characters are from DOS codepage:
 plc53.txt 14.6K