Is the expert system still in use today? In my country, the Expert System class is mandatory, if you want to take the AI specialization in most universities. In class, I learned how to make a rule-based system, forward chaining, backward chaining, Prolog, etc.
However, I have read somewhere on the web that expert systems are no longer used.
Is that true? If yes, why? If not, where are they being used? With the rise of machine learning, they may not be as used as before, but is there any industry or company that still uses them today?
Please, provide some references to support your claims.
I would say Expert Systems is still being taught. For instance, if you look at some of the open courses like MIT's, there are still lectures on it.

Also, looking at the CLIPS documentation, you will find a couple of examples of usage from 2005. 

What I suspect is that Expert Systems are now embedded with "normal systems" in practice. Hence it may be difficult to distinguish from systems used on a daily basis for diagnostics, etc. and not as popular as before.