Review Environments built on the Heroku platform, using their Review Apps functionality.
If you need to support testing and development of multi-app environments, and you're using the Review Apps Beta functionality on the Heroku platform, this is a (set of) GitHub Actions that will help you run those apps together.
We'll be trying to keep with the Heroku roadmap in order to extend the usefulness of this code. Your organization / team will need access to the ReviewApps Beta in order to use this.