Pretty similar. The main difference from the architecture standpoint is that Enterprise DC/OS uses Mesos+Marathon for container orchestration and OpenShift uses

Pretty similar. The main difference from the architecture standpoint is that Enterprise DC/OS uses Mesos+Marathon for container orchestration and OpenShift uses K8s. The other functionalities are mostly overlapping. There is also an OSS version of DC/OS minus some security features. Also, historically Mesos has had better support for running stateful workloads but K8s is catching up too. Recently, DC/OS announced support for K8s too which is similar to the K8s announcement from Docker. Disclosure: Apache Mesos committer.