You mean a spec,
and an implementation, right? ;-) (
http://github.com/tonyg/reversehttp) While I can't speak to its popularity, I'll note that it works with plain ol' HTTP, no reliance on SSH in sight, meaning building a client for the protocol is a piece of cake. If you need a client implementation focussed on something other than Ruby Rack, you could probably whip one up in an hour or so.
I personally don't think popularity or how long something has been around have much to do with the merits of technologies. Fitness-for-purpose is much more interesting.