On microcontrollers, you often don't have a standard library, or if you do, it is limited, and doesn't do things before main. The article describes pretty well what happens on a microcontroller.

I would add that in some (most?) environments, the code that gets executed before main() is easily accessible: it sits in files within the project (written in assembly most of the time).

Cool, he is talking about the loader though, which would imply that this is all language independent? Except for where he mentions things getting executed before main in C++, which I'm assuming would be the doings of the C++ standard library.

It's still pretty language independent. Qemu for instance is a c codebase that depends on static initialization functions that run before main to register the different components.

In any other context, yes, you're missing C library predecessors to main(). But it's specifically referencing embedded systems, which is why hardware initialization and memory segments are mentioned.