OpenShift is described as 'Red Hat OpenShift is a trusted, comprehensive, and consistent platform to develop, modernize, and deploy applications at scale, including today’s AI-enabled apps. Deliver better experiences faster with a complete set of services for bringing apps to market on your choice of infrastructure' and is a popular Cloud Computing service in the business & commerce category. There are more than 50 alternatives to OpenShift for a variety of platforms, including Web-based, Linux, SaaS, Windows and Mac apps. The best OpenShift alternative is Kubernetes, which is both free and Open Source. Other great apps like OpenShift are Heroku, Microsoft Azure, Rancher and Google App Engine.
CloudStack is about running virtual machines and infrastructure-as-a-service at scale. It is an alternative to OpenStack. OpenShift is a platform-as-a-service that uses Kubernates which is containers-as-a-service. So you can use OpenShift on top of CloudStack just as you can run OpenShift on top of OpenStack. So CloudStack isn't an alternative to OpenShift.