RetroArch is most popularly known for being a program with which you can play many emulators and games, which have all been customized and tailor-ported to the libretro API.
It is designed to be fast, lightweight, and portable. It tries to be on the cutting edge of technology in terms of supported technology as well as trying to be as backward compatible as possible, a paradoxical goal if any. It has features few other dedicated games / emulators have, such as:
Updated on Dec 07 2021
Full release notes are available here