NetBSD uses the GNU sort from the textutils.

What the sort manpage does not say is that it's numeric comparison does
not use atoi() or any of the normal string-to-machine conversions but
rather does it's own (admittedly fast) algorithm.

However, it does not handle leading "+"s very well, where the other ones
do.  It also does not do scientific notation.
In any case, the man page otta say this.

(This is really more relevant to the Solaris version, where the source
is not available :)