Sure there are plenty of other professions. Pilots being the first one I can think of, as they require some type of checkride (flight exam) which will include an oral examination by the instructor/interviewer. And they don't get paid for taking that checkride.

Professional musicians have to prove themselves in auditions, CPAs, auto mechanics (good ones at least), etc. The list goes on.

Professions like pilots, doctors and CPAs are bad examples because they have a certifying body that exists outside of the relationship between employee and employer. It's true they're not getting paid for that certification, but once they have it, it's valid and transferable between jobs.

Musicians and actors are better examples, as they do have auditions, but lots of actors and musicians get jobs based on their previous body of work, rather than an in-person audition.

I'm curious, can you name more professions that use what is essentially auditions for hiring, besides artist-types?

I assume you've never conducted interviews, am I correct? There are so many "developers" out there that simply can't code, regardless of what their CV or education says. 15 years experience with Java development as a senior developer but doesn't know integers have a limited size (never heard of BigInteger), knows a hash map is used for key-value but not what hash means nor what the point of an interface is? Sure, I've seen that candidate. There's just so many terrible developers that you pretty much have to do some extra filtering to weed these out.

A short technical screen to ask those things is reasonable. My post was originally about unpaid projects, although the discussion around interviewing in general has been interesting.

I wouldn't expect to get paid for a 20 minute tech trivia screen.