f.lux is a cross-platform computer program that adjusts a display's color temperature according to location and time of day.

GSmartControl is a graphical user interface for smartctl (from smartmontools package), which is a tool for querying and controlling SMART.

Open Hardware Monitor is a free open source software that monitors temperature sensors, fan speeds, voltages, load and clock speed.

Hard Disk Sentinel monitors and tests the health of your computer's hard disks.