The Autoconf suite, including M4sugar, M4sh, and Autotest, in addition to Autoconf per se, heavily rely on M4. All these different uses revealed common needs factored into a layer over M4: autom4te1.
autom4te is a preprocessor that is like m4. It supports M4 extensions designed for use in tools like Autoconf.
 Yet another great name from Lars J. Aas.