Nagios is an awesome open-source monitoring system that helps developers keep an eye on their IT infrastructure. It's an incredibly powerful tool that can check the status of applications, services, and systems, and then alert the user when something goes wrong. It's a great way to make sure that the infrastructure is running smoothly and that any problems are identified quickly. Plus, it's easy to configure and get up and running. Nagios is a must-have for any development team that wants to keep an eye on their applications and systems.