the main thing I will add is the Notification Server is the framework into which all Altiris solutions and compatible plug-ins are installed. This includes (but is not limited to): Software Delivery, Patch Management, PC Anywhere, Monitor Solution, and Recovery Solution. You also can leverage free solutions, such as HP or Dell Client Manager, or the Dell Management Console.
NS , by itself is free, however you have to pay for each of the specific solutions, or by them as a suite (Client Management, Asset Management, Server Management, etc).