pkg-config is a system for managing library compile/link flags that works with automake and autoconf. It replaces the ubiquitous *-config scripts you may have seen with a single tool.
Open source project that offer summary and download services on this page is a project that carry out their development work on other open source development sites. Their work is linked to this page via a feature called OFI, and their work is not carried out here on OSDN site.
