I think wt is much better suited than a rails clone for the few kind of webapps you'd write in C++. http://www.webtoolkit.eu/wt/

You can think of using it as a multiplatform GUI for a native app, that runs locally but uses the web browser instead of something like Qt or WxWidgets. Or you can use it for a webapp that pegs the CPU more than a database.

There's also a port to the JVM and ruby bindings.