Official site: https://letsencrypt.org/
Wikipedia: https://en.wikipedia.org/wiki/Let's_Encrypt.
Distribution specific documentation:
Gentoo: https://wiki.gentoo.org/wiki/Let%27s_Encrypt.
Installation and configuration on Gentoo / Apache
On Gentoo with the Apache web server:
Install the packages:
# emerge -a app-crypt/certbot-apache
