Caddy
Powerful, enterprise-ready, open source web server w/ automatic HTTPS
Caddy is the only web server that uses HTTPS automatically and by default. It automatically renews TLS certificates, staples OCSP responses and more. Though used mostly as an HTTPS server, Caddy can be used to run Go applications, offering automated documentation, graceful on-line config changes via API and more to these apps.
Caddy is very extensible, with a powerful plugin system unlike any other web server.