Advanced Task Killer

The Advanced Task Killer is a popular app for managing your phone's tasks and boosting its performance. It has been used by over 70 million people and can be used to kill apps and free up memory. While it does not directly speed up or save battery life, killing battery- and CPU-consuming apps may have that effect.

There are some limitations to the app, however. You cannot kill services or front apps directly - you need to ignore or force stop them. The app also has some useful features, such as an ignore list, custom item height, and one-tap widget.

To use the app, simply open it and view the running applications list. Uncheck any apps you don't want to kill, and tap the "Kill selected apps" button to kill the others. To add an app to the ignore list, long press on it and select "Ignore."

The app also offers an auto-kill feature, which allows you to choose from safe, aggressive, or crazy levels of app-killing. You can also customize the auto-kill start time.

Note that killing apps and tasks won't directly improve your phone's battery life - it's only helpful if you kill battery-hogging apps. Finally, there is a paid version of the app, Advanced Task Killer Pro, which doesn't contain ads.