  The experimental realization of a Kerr frequency comb represented the
convergence of research in materials, physics, and engineering, and this
symbiotic relationship continues to underpin efforts in comb innovation today.
While the initial focus developing cavity-based frequency combs relied on
existing microresonator architectures and classic optical materials, in recent
years, this trend has been disrupted. This paper reviews the latest
achievements in frequency comb generation using resonant cavities, placing them
within the broader historical context of the field. After presenting
well-established material systems and device designs, the emerging materials
and device architectures are examined. Specifically, the unconventional
material systems as well as atypical device designs that have enabled tailored
dispersion profiles and improved comb performance are compared to the current
state of art. The remaining challenges and future outlook for the field of
cavity-based frequency combs is evaluated.
