Recent years have seen a resurging interest in dynamical reference frames in quantum foundations, gauge theories and gravity. I will discuss some of these developments by drawing connections between the different fields. For example, I will discuss how the so-called `paradox of the third particle’ in quantum foundations can be resolved by understanding it from the perspective of boundaries in gauge theories. Conversely, I will comment on how one can understand aspects of edge modes in finite region gauge theories from the point of view of reference frames. More generally, I will explain how quantum frame covariance leads to a quantum relativity of subsystems, which entails that the notion of subsystem locality becomes dependent on the choice of frame, as do associated physical properties such as correlations and entropies. I will suggest implications of this for the interpretation of gauge-invariant observables in gauge theories and gravity.