Don’t Sleep prevents your computer from sleeping and offers a few other features related to reboot and shutdown of the computer.
Owly prevents your Mac from falling asleep and lets you customize its behavior on your machine.
Espresso prevents your Mac from going to sleep mode and has support for black and white menu bar in Mac.
If you would not like for a disk to go to sleep mode, then install Prevent Disk Sleep and it will keep your chosen disk from sleeping.
KeepingYouAwake is a retina ready app that sits in the menu bar of your Mac and lets you keep your Mac awake for as long as you want.
If your Mac automatically goes to sleep after a certain period of time, then you need Amphetamine that sits in the menu bar of your Mac and keeps your Mac from falling asleep.
If you don’t like for your Windows PC to automatically fall asleep, then you should use Caffeinated that prevents your PC from falling asleep and keeps it awake for the specified period of time.
Caffeine is a little menu bar app that prevents your Mac from falling asleep.