Regarding companies that use Prolog, here are a few examples:
A third of all airline traffic is handled by systems that run SICStus Prolog:
https://www.sics.se/projects/sicstus-prolog-leading-prolog-t...
A large portion of the New Zealand stock exchange is powered by Prolog:
https://dtai.cs.kuleuven.be/CHR/files/Elston_SecuritEase.pdf
Oracle uses Prolog in the JVM specification:
https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-0-pr...
IBM has used Prolog for natural language processing in Watson:
https://www.cs.nmsu.edu/ALP/2011/03/natural-language-process...
RedPrairie uses SICStus Prolog for optimization tasks.
Prolog is used for voice processing on the International Space Station.
http://collaboration.cmc.ec.gc.ca/science/rpn/biblio/ddj/Web...
http://smallcultfollowing.com/babysteps/blog/2017/01/26/lowe...
But are those systems responsible for all the I.T. problems that are plaguing the industry?[1] (I've been under the impression the issues were primarily with COBOL/mainframe systems, but wasn't aware Prolog was so widely used by airlines).
[1] https://www.google.com/search?hl=en&q=airline%20computer%20f...
One that was new and interesting to me is that gerritcodereview (by Google) is written in Prolog.
https://gerrit-review.googlesource.com/Documentation/prolog-...