This is the Shadow Password Suite for Linux.  This is the version
maintained by Tomasz Kloczko.

The Shadow password file utilities package includes the programs necessary
to convert traditional V7 UNIX password files to the SVR4 shadow password
format, and additional tools to maintain password and group files (that
work with both shadow and non-shadow passwords).

These tools include su, vipw, passwd, login, chsh, usermod and many more.
In addition, this provides the libmisc and libshadow libraries.