From Rosetta Code
Nawk is an implementation of AWK. Other implementations of AWK.

nawk is another name for The One True Awk, the original implementation by Alfred Aho, Peter Weinberger and Brian Kernighan.

nawk is "New Awk", and refers to the the new features from 1985. Versions from before 1985 would be oawk for "Old Awk". There is no reason to use oawk, but some systems had both, and the Heirloom Toolchest still includes both oawk and nawk.

Because of the release of source code of The One True Awk, some BSD systems now include nawk as /usr/bin/awk.