I'm compiling a Linux toolchain based on Newlib for a toy project.
Newlib's official page reports:
Newlib is a C library intended for use on embedded systems.
but without providing any particular reason.
What I'm trying to figure out is:
Unlike Glibc, which has very specific code to make sure that it is replaceable with later API compatible versions, the Newlib isn't so; nor does it support dynamic linking anyway. And it doesn't make much sense to statically link in the C library in every possible executable in a desktop environment. Therefore, Newlib is mostly suitable for embedded targets with small number of statically linked executables.
Newlib also fulfils only the parts of the C standard library and a a minimal part of the POSIX C library extensions. Specifically it doesn't concern itself with networking at all. It is somewhat debatable if anyone in their right mind, would want to build a desktop system without any networking at all, in 2017.
Another thing to note is the non-technical aspect of licensing. Glibc uses the LGPL license, which does allow linking against proprietary programs, provided that (note that IANAL) the user is able to replace the LGPL-licenced library with another one. In practice this means that either the library is dynamically linked in, or, in case of a statically linked library, the user is provided with object files that they can use to link against the replacement library to produce an executable. This means that the license itself might not be suitable for small embedded systems with proprietary software. Newlib doesn't contain any LGPL code, unless it is built for Linux targets.