While Heroku got its start from hosting Ruby on Rails applications, it nowadays supports many different environments in the Cedar stack. Node.js is what many use, but they also do support PHP. Dependency management is easy for Node.js applications as Heroku recognizes your package.json files and automatically installs the libraries needed via NPM.
Until now PHP developers haven't had this convenience, but as Composer is emerging as the default PHP package manager, I've now added support for it. Before the pull request gets accepted, Composer dependency handling can already be used by specifying my custom PHP buildpack when creating Heroku apps.
He shows you how to get it up and running with a sample application - creating the new git archive, creating the Heroku app with the custom backapack (and a "composer.json" file), setting up the main "index.php" file and push it all to Heroku. You can view his sample application here (a simple URL encoding form).