§pectre: Essential OS or program options that are hidden away in the registry or some other vague location.
I'd argue that the registry is one of the worst design mistakes of Windows, and it's definitely even more way up there if you look at the design decisions that have survived in modern Windows.
Fortunately, Linux doesn't do that, instead using text configuration files that are stored in /etc or ~/.config . Of course, there's still syntax differences between them, but at least you don't need a special program, and one file's configuration only affects the program that uses it (unless something like the password file gets corrupted).