OpenBSD has got its own ACME client, which ships by default in the base system. It has a nice config syntax, sane defaults and is well integrated with the OS.
Details:
- OpenBSD 6.1 Changelog
- acme-client(1) - OpenBSD manual pages
- g2k16 Hackathon Report: Florian Obser on httpd, networking, acme-client, and more