"Applications of delay differential equations"

I wanted to make a CW question (by the way, how to do it?).
Being interested in the mathematical theory, I was wondering if there are up-to-date, nontrivial models/theories where delay differential equations play a role (PDE-s, or more general functional differential equations).

It is clear that

-in biological (population) models usually pregnancy introduces a delay term, or

-in disease transition in networks the latent period introduces a delay, or

-in engineering in feedback problems signal processing introduces the time delay.

Would a question like this be acceptable on this site? I would like to see a list of answers where each answer contains one reference.

This post has been migrated from (A51.SE)