https://github.com/hhvm/hack-router/ and https://github.com/hhvm/hack-router-codegen/ power docs.hhvm.com and some of our other users; they do have problems such as extremely lacking documentation, which I'm going to be addressing soon.

This is definitely an area we're planning on working on - and this post is meant to be announcing the start of this work, not that it's ready :)