CoreOS is an open-source lightweight operating system based on the Linux kernel and designed for providing infrastructure to clustered deployments, while focusing on automation, ease. Developed by CoreOS, Inc
License: Free
Ubuntu Server brings economic and technical scalability to your datacentre, public or private. Whether you want to deploy an OpenStack cloud, a Hadoop cluster or a 50,000-node render farm, Ubuntu Server delivers the best value scale-out performance available. Developed by Canonical Ltd
License: Open Source
CoreOS is optimized for containerized applications and employs an automatic update mechanism, making it ideal for cloud-native environments. In contrast, Ubuntu Server is a more traditional server OS with extensive package management and community support, suitable for a wider range of applications.