Real world applications of first order logic
If you want a specific example, IBM Watson should qualify. Check the links for details on how they use Prolog. I'd say that Prolog made a huge hype in its day, and most real today's system are based on different principles rather than "first-order logic programming" in narrow sense. However, there is definitely a niche for this approach. We live in the age of other hypes, that's it.