The GitHub repository "z80-open-silicon" by user rejunity is dedicated to the development of an open-source silicon implementation of the Zilog Z80 microprocessor. The project aims to recreate this classic CPU architecture, which was widely used in desktop computers, embedded systems, and early gaming consoles during the late 1970s and 1980s. The repository includes various resources for understanding and building upon the Z80 processor design using modern tools and technologies, making it accessible for enthusiasts and developers interested in retro computing hardware or educational purposes related to computer architecture.