The LNPD and associated files are intended to allow communication of a program hosted on a Linux PC with a legOS program on an RCX.
Documentation for LNPD is unfortunately sparse. Your best bets are to read the README files below, and to poke around the archives at lugnet.com before asking questions in that forum.
The file listing below is auto-generated, showing the current list of files in this directory. To get more information about them, try the links above or download them yourself.