LibUtillery is a container for more or less unrelated utility libraries, providing functionality that is often required in both small and medium-sized software, which otherwise tends to be re-written over and over again.
The library provides a highly portable programmer's toolbox, either as-is or as a relatively easy to use code repository. It is designed to work on all kinds of modern and older flavors of Unix, as well as Microsoft Windows. Apart from requiring the "long long" integer type in one function, it is expected to be compatible with ISO C90.
Most of LibUtillery's sub-libraries could be considered a "class" that can be instantiated multiple times within a program most of the time.
IAXmodem is a software modem written in C that uses an IAX channel (commonly provided by an Asterisk PBX system) instead of a traditional phone line and uses a DSP library instead of DSP hardware chipsets.
Paul D. Smith has much information about GNU make,
including Paul's Rules of Makefiles, Advanced Auto-Dependency Generation and Multi-Architecture Builds.