Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Many, if not most, free and open source software projects are developed primarily on Linux-based systems using the GNU C Library (glibc). Projects that use glibc are likely to depend on functions that are not available on systems that use different C libraries, such as the different BSD flavors. When packages are built on systems that don't use glibc they often fail, because the other C libraries are missing functions found in glibc. The GNU Portability Library can help developers with cross-platform programming needs.
In the past there were many different libraries, such as publib, that tried to provide alternatives to the functions that are missing in the main C library. Unfortunately, handling compatibility libraries proved to be difficult. The additional libraries would require additional tests when running configuration scripts prior to compilation, and add dependencies for non-glibc systems.
As the number of new functions provided by the glibc increased, the GNU project started looking at the requirements for portability of programs on operating systems based on different libraries, and eventually created the GNU Portability Library (Gnulib) project.