  We report a new type of fluid-based driven dissipative oscillator system
consisting of a lattice of millimetric fluid droplets bouncing on a vertically
vibrating liquid bath and bound within an annular ring. We characterize the
system behavior as it is energized through a progressive increase in the bath's
vibrational acceleration. Depending on the number of drops, the onset of motion
of the lattice may take the form of either out-of-phase oscillations or a
striking solitary wave-like instability. Theoretical modeling demonstrates that
these behaviors may be attributed to different bifurcations at the onset of
instability. The results presented here demonstrate the potential and utility
of the walking droplet system as a platform for investigating wave-mediated,
inertial, non-equilibrium particle dynamics at the macroscale.
