ftrace - A function tracer for the Linux kernel.
strace - Trace system calls and signals. A diagnostic, debugging and instructional userspace utility.
Valgrind - Valgrind is an instrumentation framework for building dynamic analysis tools.
API Monitor - API Monitor is a software that monitors and displays API calls made by applications and services. Its a powerful tool for seeing how Windows and other applications work or tracking down problems that you have in your own applications
DTrace - DTrace is a performance analysis and troubleshooting tool for Solaris, Mac OS X and FreeBSD.
New Relic Browser - New Relic Browser provides deep visibility and insight into how users are interacting with any application or website.