How can this be free? If I host a massive application here, will they shut it down or rate limit or how can this work?
"The developer preview supports up to 3 gears per user. You have a quota of 40,000 files, 1GB of storage, and 512MB Memory per gear. It is free to use and you can run your application indefinitely. If you need to increase this quota, please mailto:openshift@redhat.com with your username, domain and Application URL."
from: https://openshift.redhat.com/community/faq/how-many-applicat...
Where can I get more information on Pricing ?
To get more information on the pricing and timing of a paid version of OpenShift please send an email to openshift@redhat.com
Of course, it is currently in a developer preview and so also free as in beer, but I think that's incidental--this is Red Hat after all; they actually care about users' freedom and they aren't afraid of offering paid plans and support.
Happily, since it's open source, you can just host it yourself if you aren't happy with Red Hat's potential future pricing.