Zabbix - Track, record, alert and visualize performance and availability of IT resources
strace - Trace system calls and signals. A diagnostic, debugging and instructional userspace utility.
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
ftrace - A function tracer for the Linux kernel.
Prometheus - An open-source systems monitoring and alerting toolkit.
Valgrind - Valgrind is an instrumentation framework for building dynamic analysis tools.