I've also been searching for this for years, and the closest thing I've found is Convox [1]. Unfortunately they only support AWS for now, but it's a really good PaaS on your own servers. It's open source, too [2]. You can run a convox rack without using their hosted console.

One problem is that it requires a minimum of 3 instances, so it can be more expensive than Heroku to start.

[1] https://convox.com

[2] https://github.com/convox/rack