Cockpit Project is described as 'Makes it easy to administer Linux servers via a web browser. It allows you to easily perform simple tasks like storage administration, inspecting journals, starting & stopping services, monitoring & administering several servers at once' and is a server management tool in the network & admin category. There are more than 25 alternatives to Cockpit Project for a variety of platforms, including Linux, Self-Hosted, Docker, Web-based and Mac apps. The best Cockpit Project alternative is Arcane - Docker Management UI, which is both free and Open Source. Other great apps like Cockpit Project are Webmin, Portainer, 1Panel and Coolify.
Nagios is only for monitoring servers and services whereas Cockpit is about web-based server configuration.