SpeedFan - Hardware monitor for Windows that can access digital temperature sensors located on several 2-wire SMBus Serial Bus. Can access voltages and fan speeds and control fan speeds. Includes technical articles and docs.
TechTool Pro - Techtool Pro is a robust hardware diagnostic tool available for Macintosh.
Open Hardware Monitor - Monitors temperature sensors, fan speeds, voltages, load and clock speeds, with optional graph.
DiskWarrior - DiskWarrior, the world's most advanced and highest rated hard disk, hard drive, and disk repair and data recovery tool for macOS, OS X and Mac OS X.
xScan - xScan is an application for viewing the behavior of your computer and Mac.
DriveDx - DriveDx is advanced drive health diagnostic and monitoring utility.