We had earlier posted about this tool Insomnia from MSDN, a simple WPF portable application that calls the SetThreadExecutionState API to disable sleep mode for as long as it’s running.
Mouse Jiggler is another such tool that fools your computer that you are still around by sending ‘fake or virtual’ mouse inputs, thereby preventing your Windows PC from going to sleep.
It continuously jiggles the mouse pointer to prevent screen saver activation, sleep or any such activity that may be triggered by computer inactivity.
Check the ‘Enable jiggle’ checkbox to begin jiggling the mouse; un-check it to stop. The ‘Zen jiggle’ checkbox enables a mode in which the pointer is jiggled ‘virtually’ – the system believes it to be moving but the pointer does not actually move.
You can download it CodePlex.
Also check out Insomnia & Sleep Preventer.