OCCT Perestro├»ka is a stability checking tool, free for personal use.
It comes with 4 built-in test aimed at testing CPUs, GPUs and Power supplies. OCCT also monitors in temperatures, voltages and fan speed, as well as system constants such as CPU Usage, Memory Usage and FPS (if testing in 3d).
It provides the most accurate error-detection algorithm for CPU and GPUs.
Every 15 seconds, somebody in the world launches OCCT !
OCCT Pro is designed for professionals : with it you can define a custom test composed of your own application, start a monitoring-only session, gain access to a CSV output of all readings, and customize the graph output folder (to avoid putting graphs in the end user's profile for instance).
Also, by default, all sensors will be followed in real-time to avoid missing any important information. And with the CSV output, you can run your own calculations, or design your own graphs for including the results on your website or documents.
It is available at reasonable prices, and useable in any environment, including commercial ones.