Portainer is an Australian open-source container management platform deployable from a single container, unifying Docker, Docker Swarm and Kubernetes management. The CE edition is free forever, making it one of the most popular web UIs for self-hosted container environments.
Kubernetes is the open-source container orchestration platform launched by Google in 2014 and donated to CNCF, managing large-scale container clusters with declarative orchestration and auto scaling, and is the de-facto standard for cloud-native applications.
InterWorx is a US-developed commercial server control panel offering the NodeWorx admin and SiteWorx user interfaces, with PHP 5.6 to 8.2 support, Nginx/Apache dual engines and free Let's Encrypt SSL. Lightweight and high-performance, it suits cost-conscious small hosters.
ClusterCS is a high-availability cloud server cluster management panel from Soft Dreams (Romania), building HA clusters on any cloud provider, with single servers from $7.2/30 days on hourly billing and a $70 free trial credit.