OCCT is the most popular CPU/GPU/Power Supply testing tool available. OCCT is great at generating heavy loads on your components, and aims at detecting hardware errors or overclocking issues faster than anything else. A monitoring engine is also embedded, to ease diagnostic and see how your computer reacts under heavy load using graphs.
OCCT's own CPU test. Small data set is great at pushing your CPU to its limits, and Large data set is the best at finding errors quickly
The famous Linpack test, known for pushing Intel CPUs to their limits. Not as great on AMD CPUs though, and less likely to pick up errors than OCCT
OCCT's version of the furry donut, which includes a error detection mode for finding rendering errors automatically
Exclusive OpenCL-based Memtest for testing your graphic card's memory ! Runs on any GPU (Intel, AMD, Nvidia) with OpenCL support. It is great at finding faulty bits, less at finding overclocking-induced errors
Combines CPU:OCCT and GPU:3D tests to stress your power supply and motherboard. This test is the most power-hungry included in OCCT. Useful to identify power-starved components !
OCCT will monitor your computer and present you real-time graphs showing you temperatures, voltages, fan speed, frequencies, component usage, and power comsumption during your tests.
Built-in protection for your computer
Worried about frying your components ? Turn the maximum temperature threshold in OCCT's options ! Should a component reach this critical temperature during a test, OCCT will stop itself immediately.
At the end of a test, you will be able to save a full graphical report of what happened during the test, for diagnostic purposes