The Mac (short for Macintosh) is a family of personal computers made by Apple. The Mac line began in 1984 and continues to the present day, but the brand names, processors, operating systems and development tools used on Macs have changed significantly over time.
Classic MacOS (previously simply called System Software) was the operating system preloaded on Macs from 1984 to 2001. macOS (previously called Mac OS X) is a Unix-based operating system that has been preloaded on Macs from 2001 to today.
NetHack has been available for classic MacOS since at least NetHack 3.0.5, released in 1989. It continued to be supported during the long reign of NetHack 3.4.3, but it is unknown if NetHack 3.6.4 will build or run on it. In the NetHack source code, files relevant to classic MacOS are stored in
NetHack is currently supported for modern macOS (ie Mac OS X). Since macOS is a Unix-based system, the build files are in
sys/unix, not in
sys/mac. It can be compiled with tiles, according to this discussion.