App Tamer 1.1.1 ↓

App Tamer tames applications that are chewing up excessive CPU time and battery life on your Mac. Its unique "AutoStop" feature will stop an application when you switch away from it, and then automatically restart it when you click back to it. App Tamer includes an attractive and clear user interface for managing your running applications. It shows the average percentage of your processor(s) being used by each app, and graphically displays a history of CPU usage. You can easily enable AutoStop for any application, as well as change its processing priority in OS X.

REQUIREMENTS
Mac OS X 10.5 or later.

Version 1.1.1:
Corrected performance problems caused by processes that relaunch very frequently (often without your knowledge). This change keeps App Tamer from using too much CPU time on affected Macs.
Fixed compatibility with Alien Skin Photoshop plugins.