macOS includes a "Display Calibrator Assistant" to perform some basic calibration of the built-in display.
I'm sure it's better than nothing, but how much better, I don't know.
All it immediately offers is a white point setting (I can specify a colour temperature), but after some fooling around with it I have discovered that if I launch it with an Option-click, it will provide an 'Expert mode', that will take me through a series of steps in which one adjusts sliders to make colour patches match, have squint at the display from the corner of my eye, and so on.
What other software tools - built-in, free or at least inexpensive - are available to help perform some basic calibration of the display? And, how useful are they, compared to hardware devices to do the same task?