  The ability to control the motion of mechanical systems through its
interaction with light has opened the door to a plethora of applications in
fundamental and applied physics. With experiments routinely reaching the
quantum regime, the focus has now turned towards creating and exploiting
interesting non-classical states of motion and entanglement in optomechanical
systems. Quantumness has also shifted from being the very reason why
experiments are constructed to becoming a resource for the investigation of
fundamental physics and the creation of quantum technologies. Here, by focusing
on opto- and electromechanical platforms we review recent progress in quantum
state preparation and entanglement of mechanical systems, together with
applications to signal processing and transduction, quantum sensing,
topological physics, as well as small-scale thermodynamics.
