Hmonitor is a smart hardware monitoring tool that will track and display temperatures, fan speeds, voltages and other useful information about your PCs status.
The program crams plenty of data into its small interface. Typically you'll see the temperatures of your motherboard, CPU, hard drive and graphics card; the fan speeds for your CPU, motherboard or graphics card; and the +/-12V, +/-5V, Core, Aux and +3.3V voltages on your system (as long as Hmonitor supports your hardware, and the chances are it probably does).
This information could be very useful if you've just been overclocking your system, say, and want to make sure that your system temperatures are acceptable.
But Hmonitor has other applications, too. If your system has been unstable recently, for instance, then maybe a component is overheating when it's put under strain. It's normally hard to tell, but with Hmonitor running in the background then you can assess your system's health with a glance.
Or if you'd prefer an easy life, then you can have Hmonitor take action itself when it spots that something is overheating. So the program can sound an audio alarm, execute your chosen application, or just shut down the PC to avoid the chance of any further damage: it's your call.