This article is from the MachTen & CodeBuilder FAQ, by Jaime Julca firstname.lastname@example.org with numerous contributions by others.
MachTen is a fully functional BSD system. Tenon has added a few
MachTen-specific utilities; e.g.: it can change UNIX text into text
recognizable by Macintosh applications and can cope with Apple Single/Double
file formats. In addition, a Macintosh-style MachTen Control Panel lets you
easily modify networking addresses and other system variables that would
ordinarily require editing UNIX configuration files. So, in some sense, it
is a friendlier UNIX. But, by and large, there are no surprises. MachTen is
exactly what you would expect to find on any Berkeley UNIX system.