Are there any web frameworks on top of EventMachine? So far, I've found Fastr and Cramp. Both seem to be outdated.
Moreover, Googling how to setup Rails + EventMachine, returns a limited amount of results.
NodeJS is really nothing new. Evented I/O has been around for a very long time (Twisted for Python and EventMachine for Ruby). However, what attracts me to NodeJS, is the implementations that are built on top of it.
For example. NodeJS has TowerJS. Among plenty others. Perhaps, this is one of the many contributing reasons to its trending factor.
What I like most about TowerJS, is its Rails-like structure. Is there anything like it for EventMachine?
Goliath is an open source version of the non-blocking (asynchronous) Ruby web server framework.
You may find async sinatra interesting
Besides EventMachine and the others mentioned here, there's vert.x. I'm not sure how much of a "web framework" it is, but its site shows examples for a simple app like one might write in Sinatra.