https://news.ycombinator.com/jobs is probably a good enough sample to answer that question. The answer seems to be Greenhouse and Lever.
(Some companies link to job descriptions on their own site and/or embed the ATS-hosted form in their site, but many of those use Greenhouse or Lever too. The companies linking directly to ATSes do seem representative.)
Thank you @troydavis! Greenhouse and Lever definitely seem to have the lions share (lever skewing older Y Combinator cohorts and Greenhouse newer). If you just happen to come across any newer/ up and coming ATSs, I'd love if you could update this thread (while I keep digging).
I moved my employer’s job board (previously Google Forms) to https://wrk.xyz/ a month ago.
‘Wrk’ tries to be an all in one solution and you pay when you scale hiring (each active job posting is $10/month)
Also check out https://app.ashbyhq.com/product — I haven’t used this personally, but from what I’ve seen they’ve also built out an “all in one” platform pretty quickly and are still building fast.
(Some companies link to job descriptions on their own site and/or embed the ATS-hosted form in their site, but many of those use Greenhouse or Lever too. The companies linking directly to ATSes do seem representative.)