Yes, as does riak. There are plenty of simple crdts and the theory, while recent, has all of it's fundamentals fleshed out. We know what property makes data structures crdts, and how to compose them, and how to prove they are crdts.

Currently we are in the "discovery of new crdts" and "engineering and implementing of older crdts reliably" phase, and in some cases "discovering when not to use crdts".

The crux of the this issue is that crdts that play nice with human expectations in regards to collaborative document editing are not known, possibly excepting automerge (yjs). As it's a 'softer' concept will no good axioms, there is no solid theory on how to combine the theoretical requirements of crdts with human expectations.