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.
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 
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.