Our detectives are back with the following intel on this WordPress site
The site is using the Editor Redux theme by Automattic Team 51 + Array Themes .
We could identify 2 plugins (there might be more) -
Jetpack by WordPress.com
This information was last updated 14 April, 2017
Editor Redux is a fork of Array's Editor theme, with some customizations made for joelonsoftware.com.
Batcache uses Memcached to store and serve rendered pages.
Jetpack gives you tools to design, secure, and grow your site in one convenient bundle.