From Forum Nokia Wiki

TaskSpy is a task manager for Symbian OS devices. It allows you to get more control and information over running tasks on your mobile phone. You can quickly switch tasks, kill processes and threads or free unused memory, as well as display detailed information about system resources. Other features, such as tracking cpu load and free memory, though aimed to developers, may result of interest to advanced users.

TaskSpy is freeware and available for Series 60, Series 80, Series 90 (Nokia 7710) and UIQ devices.

source code:

• TaskSpy v0.96 source code
• TaskSpy v0.96 source code (including partial port to S60 3rd edition)

• Another Task Manager Example