The "ptrace" system call provides a way to control a running process, such as catching system calls. This module is specific to the FreeBSD operating system on the Intel 386 processor.
I came to this module after trying fairly unsuccessfully to work out how to call the poorly-documented FreeBSD ptrace. I was looking for an example of ptrace in C. As it happens, Dan Kogai's Perl module was the best thing available for information on these functions. I ended up unwrapping Dan's Perl example into C.
Besides that, it's also a very useful module in itself, if you need to access ptrace in FreeBSD.