  Although reconfigurable intelligent surfaces (RISs) have demonstrated the
potential to boost network capacity and expand coverage by adjusting their
electromagnetic properties, existing RIS architectures have certain
limitations, such as double-fading attenuation and restricted half-space
coverage. In this article, we delve into the progressive development from
single to multi-functional RIS (MF-RIS) that enables simultaneous signal
amplification, reflection, and refraction. We begin by detailing the hardware
design and signal model that distinguish MF-RIS from traditional RISs.
Subsequently, we introduce the key technologies underpinning MF-RIS-aided
communications, along with the fundamental issues and challenges inherent to
its deployment. We then outline the promising applications of MFRIS in the
realm of communication, sensing, and computation systems, highlighting its
transformative impact on these domains. Lastly, we present simulation results
to demonstrate the superiority of MF-RIS in enhancing network performance in
terms of spectral efficiency.
