This is kind of the wrong question. You can trivially run openstack ontop of mesos and vice versa.<p>Mesos is bigger on services, openstack is bigger on virtual machines. They are different solutions for overlapping, but fundamentally different problems.<p>Here is an example of Ebay running mesos ontop of openstack:<p><a href="http://www.ebaytechblog.com/2014/04/04/delivering-ebays-ci-solution-with-apache-mesos-part-i/#.U9qEHnVdWEJ" rel="nofollow">http://www.ebaytechblog.com/2014/04/04/delivering-ebays-ci-s...</a>