Automated letsencrypt/certbot certificate request and deploy script for Zimbra hosts.

Let's Encrypt for VMware ESXi with easy installation using pre-built VIB or offline bundle. Auto-renewal of certificates.
w2c-letsencrypt-esxi is a lightweight open-source solution to automatically obtain and renew Let's Encrypt certificates on standalone VMware ESXi servers. Packaged as a VIB archive or Offline Bundle, install/upgrade/removal is possible directly via the web UI or, alternatively, with just a few SSH commands.

An ACME-based certificate authority, written in Go.
This is an implementation of an ACME-based CA. The ACME protocol allows the CA to automatically verify that an applicant for a certificate actually controls an identifier, and allows domain holders to issue and revoke certificates for their domains. Boulder is the software that runs Let's Encrypt.

minica is a small, simple CA intended for use in situations where the CA operator also operates each host where a certificate will be used. It automatically generates both a key and a certificate when asked to produce a certificate. It does not offer OCSP or CRL services. Minica is appropriate, for instance, for generating certificates for RPC systems or microservices.

The HTTP/2 Web Server with Fully Managed TLS (automatic HTTPS).

Caddy 2 is a powerful, enterprise-ready, open source web server with automatic HTTPS written in Go

• Caddy @ GitHub.
• Exploring Caddy, An Open Source Web Server @ Dan on Open Source Software's YouTube.

Hitch is a libev-based high performance SSL/TLS proxy by Varnish Software.

SSLMate is the easiest way for developers and sysadmins to buy SSL certificates.

Let’s Encrypt is a new Certificate Authority:
It’s free, automated, and open.