Awesome! IMHO it was more of a refinement of the concept of deploying each commi...

Awesome! IMHO it was more of a refinement of the concept of deploying each commit; doing it at a PR and push level worked better. Open-sourcing it, and getting Heroku to bake it in was the icing on the cake for us!

Context for everyone else: early 2014 we open-sourced https://github.com/rainforestapp/fourchette, which was an pioneer of Heroku Review Apps (https://devcenter.heroku.com/articles/github-integration-rev...), and generally the concept of doing this on pull requests over just per branch or commit.