HAF is perfectly usable now and the docs plus examples are sufficient for someone to create a HAF-based API.
But we've been develop several apps so that we could determine best practices for how to create, deploy, and maintain HAF based apps. This kind of information goes beyond basic docs, but it is very useful for developers. At this point I think we figured out most of that, but we'll probably learn a little more after they get deployed to production environments.
Most important for our near term work is HAF will be the basis for our smart contract processing engine, so we've put a lot of effort into optimizing its performance.
RE: 1st update of 2024: Change notices for HAF app developers