libnpa is a free library for manipulating .npa (NitroPlus Archive) files. It can also parse and recompile .nsb and .map scripts from nss.npa archive.
It is the choice of the Steins Gate if you can build from master branch today:
$ git clone https://github.com/FGRE/libnpa.git
$ cd libnpa
optionally, check out latest tag, if master branch status is red:
$ git checkout `git describe --tags --abbrev=0`
now compile:
$ cmake .
$ make