Whatever version of Windows you are using, the built in Task Manager tool can be used to monitor and control running programs and processes, giving you the option of closing anything which is proving to be problematic or unstable. DTaskManager Portable is a free alternative that grants you even greater control over your computer and comes with the added benefit of running from a USB drive.
The utility provides you with three different ways of terminating programs and process you no longer need to be running. The standard method sends a request to the process and attempts to perform a regular, neat termination. You can also use a forced termination if this fails to work, but this could be interrupted by a dialog box generated by the application.
DTaskManager Portable gives you the option of performing an advanced forced termination which will close any application or process and ignore any dialog that may be generated. A handy feature of the program is the option of selecting multiple programs and processes so they can all be terminated in one fell swoop.
If you are trying to balance system resources when carrying out a hardware intensive task, the option to pause and resume processes will prove very useful. This enables you to suspend any tasks you do not need to be running right now so you can concentrate on something else, before resuming from where you left off.
A couple of handy options that are not already offered by Windows, but this is not a tool that is going to be used every day.