Jeff Lindsay wrote https://github.com/progrium/dokku which uses Heroku Buildpacks to build an app and then run it using Docker - it is a very neat little tool : )
Very true, this would be more compelling if Heroku got behind the project themselves because their build packs would be very portable and possibly a future standard.
It seems that Docker is becoming the container of choice but how apps are layered on top is still very much up for debate.