Bit of self-promotion, but Milvus (https://milvus.io) is another open-source vector database option as well (I have a pretty good idea as to why it isn't listed in a16z's blog post). We also have milvus-lite, a pip-installable package that uses the same API, for folks who don't want to stand up a local service.

    pip install milvus

Other than that, it's great to see the shout-out for Vespa.