Create an account at http://openshift.redhat.com/
Then do
rhc app create etherpad nodejs-0.10 mongodb-2.4 --from-code=https://github.com/wshearn/etherpad-example.git
That's it, you can now checkout your application at (default admin account is admin/OpenShiftAdmin):
http://etherpad-$yournamespace.rhcloud.com