Apple System Profiler is a Utility that ships with the MacOS

Within the main window, there are 6 tabs: System Profile, Devices and Volumes, Control Panels, Extensions, Applications, System Folders.

The "System Profile" tab contains information on the Macintosh it is running on, such as the current OS it is running, filesharing status, disk cache, virtual memory, physical memory, VRAM, L2 cache, processor MHz, computer model, and various network configuration information.

The "Devices and Volumes" tab contains information on what is connected to the ATA, SCSI, PCI, and (on PowerBooks) expansion bay.

The "Control Panels" tab shows all the control panels that are currently loaded, and gives a brief description of each.

The "Extensions" tab shows all the extensions that are currently loaded, and gives a brief description of each.

The "Applications" tab shows all the applications that are currently loaded, and gives the version, memory size, file size, whether or not it is an apple application, as well as a brief description of each.

The "System Folders" tab shows what system folders you have on your computer, and tells what system version they are.