Have you looked at http://www.chicagoboss.org? "Chicago Boss is the answer to slow server software: a Rails-like framework for Erlang that delivers web pages to your users as quickly and efficiently as possible."
I played with it and found it to be pretty Rails-like, even including several moments of "what foul sorcery is this?"
Generally, new stuff that is successful does not compete head-on, unless it's got some kind of "unfair advantage" like a big company behind it. In other words, it does something a bit better, but also differently. Rails was better organized and cleaner than PHP, but less bureaucratic than Java.
Chicago Boss can't compete with all the users and plugins and everything that Rails has, head on, so it's probably best used where it has an advantage on Rails: stuff like websockets where holding a lot of them open is a piece of cake for Erlang, but more of a resource hog for Rails (at least it used to be that way, has 4 improved things?).
Chicago Boss might fit the bill for you; I tried it and found it felt like it was trying to force a foreign model on Erlang a little too hard. I ended just putting something together myself with cowboy and other pieces like erlydtl, and ended up quite happy with it.