procexp.exe is process explorer. It is an expanded version of task manager. More information can be found here.

The Process Explorer display consists of two sub-windows. The top window always shows a list of the currently active processes, including the names of their owning accounts, whereas the information displayed in the bottom window depends on the mode that Process Explorer is in: if it is in handle mode you?ll see the handles that the process selected in the top window has opened; if Process Explorer is in DLL mode you?ll see the DLLs and memory-mapped files that the process has loaded. Process Explorer also has a powerful search capability that will quickly show you which processes have particular handles opened or DLLs loaded.