Hg

This is:

Hg - Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum (from "hydr-" water and "argyros" silver).

No, this is:

Mercurial is a distributed version control system. Mercurial is dedicated to speed and efficiency with a sane user interface. It is written in Python.

How to get.

cd /usr/ports/devel/mercurial
make install clean

or just

pkg_add -rf mercurial