$ heroku plugins:install https://github.com/ddollar/heroku-anvil

{
  "README.md": {
    "mtime": 1339185087,
    "mode":  100644,
    "hash":  "0000000000000000000000000000000000000000000000000000000000000000"
  },
  "lib/web.rb": {
    "mtime": 1339185087,
    "mode":  100644,
    "hash":  "0000000000000000000000000000000000000000000000000000000000000000"
  }
}

$ curl -X POST https://anvil.herokuapp.com/manifest \
       -d "manifest=$(cat manifest.json)"
{"id":"00000000-0000-0000-0000-000000000000"}

$ curl -v -X POST https://anvil.herokuapp.com/manifest \
       -d "manifest=$(cat manifest.json)" \
       -d "buildpack=https%3A%2F%2Fbuildkit.herokuapp.com%2Fbuildkit%2Fdefault.tgz" \
       -d "env={'FOO':'bar'}"
* Connected to anvil.herokuapp.com (107.20.215.233) port 443 (#0)
> POST /manifest/build HTTP/1.1
< HTTP/1.1 100 Continue
< HTTP/1.1 200 OK
< Content-Type: text/plain
< Transfer-Encoding: chunked
< X-Slug-Url: http://localhost:5000/slugs/00000000-0000-0000-0000-000000000000.tgz
< Connection: keep-alive
<
Launching build process... done
Recreating app from manifest... done
Fetching buildpack... done
Detecting buildpack... done, Buildkit+Ruby
Compiling app...
...

$ curl -X POST https://anvil.herokuapp.com/manifest
       -d "manifest=$(cat manifest.json)"
["0000000000000000000000000000000000000000000000000000000000000000"]

$ curl -X GET https://anvil.herokuapp.com/file/0000000000000000000000000000000000000000000000000000000000000000
file data here
…

$ curl -X POST https://anvil.herokuapp.com/file/0000000000000000000000000000000000000000000000000000000000000000
       -F data=@myfile
"ok"