m4r is available only as a gzipped tar file containing all of the source files necessary to build and install the program.

To build and install m4r, download this file, and then run the GNU gunzip program on that file (to uncompress it) and then run GNU tar on the resulting .tar file to un-archive the various source files. Then look within the m4r-1.4 directory which will be created when you un-tar the sources and read the README and INSTALL files for further instructions on building and installing m4r.