The advantage of Nano is that it is written in C, has zero required dependencies other than libc, and the compiled binary is 200 kilobytes. This makes it possible to include it in the base system, even on very tiny distros.
(I get "no dependencies", but that seems orthogonal to being written in C. Specifically, what does C bring that isn't minimal dependencies, or a small binary?)
ExcelsiorJET, JamaicaVM, Aonix PERC, IBM Websphere Real Time, Xamarin on iOS, .NET Native, Bartok.
In the context of nano and editors, you also have to contend with POSIX, tty I/O, etc.
This matters more for distros and OSes where building things from source - either everything, as in e.g. Gentoo, or at least the base system, as in the BSDs - is pretty common and expected.
the C standard library?
The advantage for whom? Surely not the user.
(True story - A5000 with RISCOS back in about 1993)
(Zap wins, of course!)
I'd love a working replacement for Sublime Text written in Go rather than all of these Electron based editors. Lime Text is kind of alpha quality.
Coincidentally, code written in C doesn't have that problem.
Stability is guaranteed on userspace API level - e.g. libc. So well-behaving apps are supposed to just use that, and let it handle syscalls. But Go doesn't.
The system libraries like libc themselves use syscalls internally, yes. But on those platforms I'm talking about, they're maintained by the same people who maintain the kernel, and both components are versioned together. So they can go and change a syscall, and then also make the corresponding change to libc (without changing the latter's public ABI), and ship the updated versions together as the new OS release. Well-behaved apps dynamically link against libc, so the change is completely transparent to them.
On Linux, different people maintain the kernel and libc (and, in fact, there's no single officially blessed libc - this is one case where the old adage that "Linux is just a kernel" is in full force). Consequently, the interface between the two has to be treated as a public API, with stability guarantees.