Deep Learning that Doesn't Involve Neural Networks?

Hey everyone,

I've been delving deeper and deeper into this deep learning rabbit hole (harharhar). For all intensive purposes it seems like everything I come across is a variant of a neural network. Different structure, different cost functions, so on, but a neural network nonetheless.

So, just for curiosity's sake, are there any models/techniques out there that aren't neural-network based?

edit: Still learning more about the English language apparently, really thought "intensive" was an idiom, not "intents and purposes" :)