There are many examples of driven, non-equilibrium systems that spontaneously break the temporal symmetries of the driving force :

- The Faraday instability is often viewed as the quintessential example of a subharmonic instability in a spatially extended system.
- A flag fluttering in the wind executes periodic motion even when the upstream wind is steady.
- A fluid layer heated sufficiently from below spontaneously develops convective rolls and even traveling waves. Both break the spatial and temporal symmetries of the imposed temperature gradient.
- Complex mixtures of chemicals can break spacetime symmetries in remarkable ways. Uniform oscillations can spontaneously emerge, as can rotating spiral waves and labyrinthine patterns.
- And for a simple demonstration that a parametrically forced pendulum exhibits a subharmonic response, one need only consider the problem made famous by Joseph Keller: the sideways swing of the ponytail on a jogger whose head moves up and down as she runs.

Floquet time crystals do have features that distinguish them from classical systems displaying broken time-translation symmetry; they are closed quantum systems (?? en contradiction avec wiki ??), and as such the issue of heating under external forcing is highly nontrivial. They also have spatiotemporal long-range order. The complete absence in the original time-crystal literature of references to any of the classical systems, particularly Faraday waves, represents an important missed opportunity.