[jvc26]

Whilst it doesn't tell you about the stack it's running on, the site code is open source: https://github.com/4clojure/4clojure

[pangram]

Looks like mongodb + compojure + some other interesting libraries (clojail for protected eval, for example), running on a Linode.

[Rayne]

This is correct. It is worth noting that our setup is hardly complex or clever.