Hardware Lister - lshw (Hardware Lister) is a small tool to provide detailed information on the hardware...
Activity Indicator - A HDD and SSD virtual LED program which can stay on system tray and display disk activity.
iStat Menus - "An advanced Mac system monitor for your menubar."
DiskLED - DiskLED is a flexible hard disk and general system activity indicator system tray applet.
Speccy - Speccy - find the details of your computer's specs. Great for spotting issues or finding compatible upgrades. Download the latest version free.
Atlas Hard Drive LED - Atlas Hard Drive LED is a system tray utility program that allows the user to always be aware of whether their hard drive is reading or writing. The system tray icon will change to the color red when the selected hard drive is processing.