H2O Wave has a similar (probably tinier) Grammar of Graphics API: https://wave.h2o.ai/docs/plotting

Leland Wilkinson (GoG inventor) and I designed it together a couple of years back.

The function for creating marks (a layer) tries to be as "flat" as possible, in the sense that it should be possible to render most common kinds of plots without having to pass nested/hierarchical options: https://wave.h2o.ai/docs/api/ui#mark