Wrote a custom libc for POSIX and x86-64

What motivated your choice to make a single-header libc?

How much of libc does it cover? How it’s different from libc?

At a quick glance, it's missing at least malloc(3) and printf(3); I'd guess much more besides.

What do you mean by "for POSIX"?

Why have you posted a link to an empty README?

And just... why?

I don't know why the down votes here... Maybe the last question?

POSIX mandates various header files; it is not possible to implement a single-header library in a POSIX compliant manner. Plus this library implements the ANSI c standard library and contains none of the POSIX c things like nl_types and so forth. It is definitely a confusing description.

Technically you could symlink all required POSIX header names to a single physical header.

Sure, but this library contains none of the contents of any of those headers, so it still doesn't apply here