Dynadot auction off the expired domains - have picked a few pending delete/drop ccTLDs for projects there.
Numerous registrars pipe off domains which are not renewed to GoDaddy, ISTR enom has their own expiring/expired platform .
gTLDs often get sold at 2-4 weeks from expiry rather the drop, with some like namebright/hugedomains making a serious business out of it.