That's a limitation of Rails, not Ruby. One could use Node.js in the same manner. Ruby has been doing async I/O in the form of EventMachine longer than Node.js has even existed.
NodeJS builds on some C async framework, so pretty much every language build on C could go the Node route - but it would be a lot of work. Personally I wish somebody would adapt it for Arc - or maybe not, so that if I ever apply to YC again I can do that for bonus points :-)
EventMachine is OK, I suppose, but I have heard that it has some warts. Are there any good web frameworks that build on EventMachine? Though I suppose the basic Sinatra-Style framework would not be that hard to build...
