PowerPlanner
A lightweight utility that lets you switch between two Windows Power Plans either automatically based on current CPU utilisation or manually using the system tray icon.
Why would you want this? Most every day tasks such as webbrowsing aren't very taxing on the CPU. Using the Power Saver plan for these task will mean many systems (laptops especially) run cooler and quieter without any real any real performance hit. But when gaming or rendering a video you naturally want as much out of your CPU as possible.
Switching manually through Windows is a bit tedious, but PowerPlanner can switch Power Plan for you based on current CPU utilisation. Or you can do it manually through the system tray icon.
By default PowerPlanner checks the CPU utilisation every 5 seconds and switches to the chosen performance plan if utilisation is above 20% and drops back down to the default plan if it falls below 10%
Download
PowerPlanner is written in AutoHotkey. The download includes both the plain AutoHotkey script and a compiled exe file.