The real estate NAR MLS listing services has(/had) a monopoly. There was only a single provider, you had to be a realtor to manage it, and realtors colluded to penalize offerings (like FSBO's) that weren't managed through realtors.
What Craigslist category is equivalently anticompetitive? Real estate? That's NAR. Rentals? Craigslist may have 50% of that market. Jobs? Craigslist trails all the major jobs sites.
