Caddy is a lightweight, general-purpose web server for Windows, Mac, Linux, BSD and Android. It is a capable alternative to other popular and easy to use web servers. (@caddyserver on Twitter)
The most notable features are HTTP/2, Let's Encrypt support, Virtual Hosts, TLS + SNI, and easy configuration with a Caddyfile. In development, you usually put one Caddyfile with each site. In production, Caddy serves HTTPS by default and manages all cryptographic assets for you.
See: website 
The Let's Encrypt integration is interesting, not only does the server default to HTTPS, it will fully manage the relevant cryptographic assets for you. Initially, automated certificate renewals would see the server do a graceful restart when a certificate was renewed. A recent version see an end to these automatic restarts, and also adds 'On-Demand TLS' where certificates can be obtained on demand during TLS handshakes.