Open Hardware Monitor - Monitors temperature sensors, fan speeds, voltages, load and clock speeds, with optional graph.
AQI - Get air quality updates in your menu bar.
Guru3D - Guru of 3D: PC Hardware Reviews and tests
CheckMyMac - Hardware and System usage monitor for MAC OS X Intel 64 10.8 +
Geforce Experience - GeForce Experience is a new application from NVIDIA that optimizes your PC in two key ways.
CPU-Z - CPU-Z is a freeware that gathers information on some of the main devices of your system : Processor name and number, codename, process, package, cache levels.