  Engineered quantum systems enabling novel capabilities for communication,
computation, and sensing have blossomed in the last decade. Architectures
benefiting from combining distinct and complementary physical quantum systems
have emerged as promising platforms for developing quantum technologies. A new
class of hybrid quantum systems based on collective spin excitations in
ferromagnetic materials has led to the diverse set of experimental platforms
which are outlined in this review article. The coherent interaction between
microwave cavity modes and collective spin-wave modes is presented as the
backbone of the development of more complex hybrid quantum systems. Indeed,
quanta of excitation of the spin-wave modes, called magnons, can also interact
coherently with optical photons, phonons, and superconducting qubits in the
fields of cavity optomagnonics, cavity magnomechanics, and quantum magnonics,
respectively. Notably, quantum magnonics provides a promising platform for
performing quantum optics experiments in magnetically-ordered solid-state
systems. Applications of hybrid quantum systems based on magnonics for quantum
information processing and quantum sensing are also outlined briefly.
