[dschatz]

You can look at OSkit as one attempt to do this. I think the overwhelming reason its not common is that no one wants to build an OS. If they do it's for the educational experience not practical use. This means hobbyists aren't interested in just using a framework.

[qznc]

I am not sure what exactly is meant by "Ruby on Rails of kernel". Probably "an opinionated framework to build your own kernel". In this case OSkit is probably the best answer to the question. Maybe look at micro- and exokernels.

[dschatz]

I think another problem is that an OS is not analagous to a website, it's more analagous to a web framework. And it's not like there are any framework building frameworks floating around