This is a Heroku buildpack for Heroku apps that wish to build themselves.
It expects the app to provide the usual buildpack executables in its source tree, in a directory named "bin" in the top of the git repo; this is the same interface all other buildpacks provide. See the buildpack documentation for more details about this interface.
Thus, an app serves as its own buildpack.
Phil Hagelberg originated this lovely idea.
$ find . -type f -print
./bin/compile
./bin/detect
./bin/release
./bin/run
./Procfile
$ cat Procfile
work: bin/run
$ heroku create -s cedar
...
$ heroku config:add BUILDPACK_URL=http://github.com/kr/heroku-buildpack-inline.git
...
$ git push heroku master
...