An Application Performance Management (APM) tool is a program that allows you to monitor the behavior of your software systems. APM tools can be used to record data about response times of certain pages, resource utilization of critical systems, and much more. Some of them allow you to set up thresholds that, when exceeded, send alerts. They are a great way to analyze and optimize your application.
If you'd like, you can push the load testing results that you get from Flood onto the APM tool that you're already using, providing a one-stop shop for everything related to your application performance. This may also make it easier to investigate potential bottlenecks revealed by load tests by allowing you to cross-reference events and times with logs from related servers.