Caffeine for Windows - Prevent your computer from going to sleep
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.
Caffeine for Linux - Inspired by the Mac OS X version, Caffeine for Linux is a status bar application able to...
Open Hardware Monitor - Monitors temperature sensors, fan speeds, voltages, load and clock speeds, with optional graph.
Caffeine for Mac - Caffeine is a tiny program that puts an icon in the right side of your menu bar.
xScan - xScan is an application for viewing the behavior of your computer and Mac.