Insomnia is a free tool which can temporarily stop your PC sleeping or hibernating.

The program arrives as a single executable - not even in a zip file - and goes to work as soon as you launch it, preventing your PC shutting down even if it seems to be idle.

This sounds a very familiar idea, but Insomnia takes a much smarter approach than most of the competition. It doesn't fake keypresses or mouse-clicks, which may cause problems with other applications, and it doesn't persistently change system settings. Instead the program works with Windows APM (Advanced Power Management) flags, preventing your system ever realising it's time to shut down.

Right-clicking Insomnia's system tray icon displays just two options: "Keep Monitor On" to toggle its stay-awake function on or off, and "Exit" to close it down.

It's all very simple and lightweight, too. CPU usage is minimal and the program used barely 1MB RAM on our test PC.