An Open Source, Self-Hosted Heroku
We at Globo.com[1] are using docker in production before it was considered ready for prod, with tsuru PaaS, as some features in tsuru(like self-healing) made docker easy to handle, manage and scale containers. Tsuru has more than 4 years, it's really stable and reliable, we are attending huge traffics in a large number of apps and it has lots of important features like multi cluster(pool), metrics, auto scale, granular in relation to permissions of users, etc. We are investing a lot in this project as anyone can see in our repo[2] and we changed completely the way devs, (dev/)ops and product people worked here. 
Tsuru was already easy to install(all in one VM[3,4]), and now we have an experimental way[5] to make it in all IaaSs supported by docker machine.[1] Globo.com is the internet arm of Globo Group, the biggest broadcast television in Brazil and second in the world
[2] https://github.com/tsuru/tsuru
[3] https://github.com/tsuru/tsuru-bootstrap
[4] https://github.com/tsuru/now
[5] https://docs.tsuru.io/stable/experimental/installer.html