A backend for Meteor, fronted in another language doesn't exist. What I'll assume you're looking for is a bridge. Which Meteor.JS provides access to via the Distributed Data Protocol (DDP). There are clients for most languages, from javascript to ruby and etc. However, there are no servers operating the DDP outside of Meteor to the best of my knowledge. The DDP itself is kind of like REST over sockets on steroids.
https://github.com/meteor/meteor/blob/devel/packages/livedat...