> My favourite is thttpd [1] which is super tiny, battle-tested and actually meant for the job (and only this job). It's available as a package on most Linux distros.
There are times that I want to run Let's Encrypt that's not a full-time web server (SMTP, IMAP, etc), and it would be handy to spin up something ad hoc on tcp/80 to do the verification step and then stop it right after.