Heroku push rejected, no Cedar-supported app detected
I had a similar problem, but with Django (incorrectly named "requirements.txt"). I think to generalize the other answers here, when you get this error it's because Heroku is missing some key file that it uses to identify your app (and its type).
- php: index.php
- python: requirements.txt
- ruby: Gemfile # note the capitalization
- node: package.json
I ran into this error message, but my problem was that my rails app was not in the root directory of my git repo. After I moved the files into the root dir, everything worked.