It’s not a new project, but if you never heard about it, have a look at Swiftiply :
"Scaling your web applications should be easy. Start small, then when you need more capacity, just add it. Another process. Another machine. More capacity, instantly. Without additional configuration or software restarts. That is what you get with Swiftiply. Swiftiply is a backend agnostic clustering proxy for web applications that is specifically designed to support HTTP traffic from web frameworks. It is a very fast, narrowly targetted clustering proxy. In back to back comparisons of Swiftiply to HAProxy, Swiftiply reliably outperforms HAProxy (tested using IOWA, Rails, and Ramaze backend processes) and, depending on your web framework, you may not even need to put a traditional web server into your architecture at all. Swiftiply is a clustering proxy server for web applications. What makes it different from other clustering proxies, however, is that it expects the backend processes to connect to it. That is, the backend processes are clients of the Swiftiply server, as are the browsers out in userland. The advantage of this is that it permits the back ends to maintain a persistent connection with the proxy server, which eliminates socket setup/teardown costs. And even more importantly than that, it permits backend processes to be started up or shut down without requiring any notification or configuration of the proxy. So, if more capacity is needed, all one needs to do is start the processes. It will immediately be available and will begin to be utilized."
I finally tested it with Rails and it works as advertised. Performance is immediately doubled, and it’s a breeze to install. Swiftiply rocks.