It turns out that there are actually quite a few companies that offer a service like this available freely (at least somewhat) through an API, so I set out to try them all out and assess their quality and suitability for my project. Most of these APIs are provided by companies that do various things in the NLP (natural language processing) realm and/or work with large semantic datasets. Many of the APIs provide a variety of information, only some of which is the set of entities that I’m looking for, so they may have good features that are excluded from my narrow comparison.