That's “non-open open source”, with two opens.
In other words, it's the Cathedral model.
“Or you could even find somebody who is willing to transport 10 cars at once, for less than it would cost you to go get that car yourself.”
which the manufacturer can finely handle by itself. The only situation where such middle-men could contribute to lower logistic costs is when the factories of different manufacturers are all in the same spot.
“Some of the comments use font size 0.85rem (never heard of REM before for a font size), and some of them use 1.5em. Can't work out why some are different. Don't care either. ”
This page explains why you should avoid em, unless you know what you're doing. Most of the time, you want to define the size of a font in terms of the default size, not in relative to parent element.
You have a very interesting definition of "most popular".
MS Excel is indeed popular, but I think it's rather due to its level of polishedness rather than customizability. (Unless you consider cell formulas as customizability as well)