Caffeine for Windows - Prevent your computer from going to sleep
Caffeine for Mac - Caffeine is a tiny program that puts an icon in the right side of your menu bar.
KeepingYouAwake - A Caffeine clone for macOS Yosemite, El Capitan and Sierra (including Dark Mode).
Caffeine for Linux - Inspired by the Mac OS X version, Caffeine for Linux is a status bar application able to...
Econap - Put your PC to sleep when it's really idle
StellaWake - Utility software for Windows PC to prevent sleep status when the system is being used by network, CPU or disk.