wadptr is a tool for compressing Doom .wad files. It takes advantage of the structure of the WAD format and some of the lumps stored inside it to merge repeated data. The manpage has some more information.
Building wadptr requires a toolchain with at least C99 and POSIX.1-2008 support, plus GNU make. Contemporary systems based on Linux, BSD, Solaris/Illumos, Cygwin or mingw-w64 will do.
"You should have used WADPTR" - unhappily dshrunk fraggle