libpng supports the PNG (Portable Network Graphics) format files. It was designed as a replacement to GIF files, with many improvements and extensions, as alpha channels (variable transparency), gamma correction (cross-platform control of image brightness) and two-dimensional interlacing (progressive display).
Mesa is a 3-D graphics library with an API which is very similar to that of OpenGL. To the extent that Mesa utilizes the OpenGL command syntax or state machine, it is being used with authorization from Silicon Graphics, Inc(SGI). However, the author does not possess an OpenGL license from SGI, and makes no claim that Mesa is in any way a compatible replacement for OpenGL or associated with SGI. Those who want a licensed implementaion of OpenGL should contact a licensed vendor.
The PCRE library is a set of functions that implement regular expression pattern matching using the same syntax and semantics as Perl 5. PCRE has its own native API, as well as a set of wrapper functions that correspond to the POSIX regular expression API. The PCRE library is free, even for building proprietary software.
Wayland is a protocol for a compositor to talk to its clients as well as a C library implementation of that protocol. The compositor can be a standalone display server running on Linux kernel modesetting and evdev input devices, an X application, or a wayland client itself. The clients can be traditional applications, X servers (rootless or fullscreen) or other display servers.