At the heart of everything is Ring[1]. Ring is roughly equivalent to WSGI or Rack. However, if you use Django in python you basicly dont ever have to know about WSGI. In Clojure you do want to know about Ring. Thankfully Ring is very simple; its a spec describing request maps and response maps. In addition provides common adapters for various JVM web servers (In the general ring ecosystem there is support for Jetty, Netty (via Aleph/Lamina), Google App Engine (via appengine magic), Servlets, Mongrel2) and middlewares.
There are three sets of libraries on top of ring that are commonly used to build sites:
## Moustache
Probably the closest to raw ring of the three, moustache provides a sophisticated url routing API. Of the three I'm mentioning here it is probably the least suitable for clojure beginners, however it is my personal favorite.
## Compojure
This was the most popular [noir is apparently on par] and oldest (it predates ring but was rewritten ontop of it in the 0.4.0 release). The best analogy here is apparently sinatra for ruby.
## Noir
Noir is the most recent addition and is higher level than Moustache or Compojure. In fact, Noir is built on Compojure. I havent had any real experience with Noir myself but it is probably the easiest entry point into web programming in clj.
Compojure and Noir both use Hiccup for HTML generation, and Moustache uses Enlive. Enlive is extremely powerful; even if you choose hiccup I would encourage you to take a good look at enlive anyway, the two solutions dont need to be mutually exclusive.
[1] Ring: http://github.com/mmcgrana/ring/I'm not sure there is a rails really and I think that's somewhat by design. Compojure is probably the most famous Clojure web lib, but it's not a framework per se. It's at a level below web-frameworks as most people think of them and Noir is actually built on top of it.
If you're just wondering in terms of having an active community, I believe Noir is currently the most trafficked complete package, but Compojure itself draws a lot of discussion :)
Citation needed.
tl;dr What is the equivalent of rails in the clojure community?