Your license will never expire

Also after initial purchase of any license you are eligible to update your software at no cost for 6, 8, 12 or 24 months. Additionally, after free updates period expires, you will be eligible for any new releases and updates at special low prices.

Service Provider License

SPL license allows service providers to deliver monitoring solutions to end customers on a rental, subscription or services basis. You may make Software functionality accessible to your end users in an extranet deployment.
For example you may install HostMonitor and Web Service on your own systems and install Remote Monitoring Agents (RMA) and Remote Control Consoles (RCC) on systems that belong to your customers.

Enterprise license, Long Term Support

Long Term Support option allows you to receive support and updates within 4 years after purchase. Any update for every component of this software, including additional tools and/or utilities that may be added to the Enterprise package in the future will be available for you at NO COST.
100,000 test items means you can monitor pretty large networks, e.g. ping 100,000 systems or setup 20 different checks for each of 5,000 servers.

What "test item" means?

Consider for example a simple situation: you need to monitor 6 parameters on 80 servers (e.g. you need to monitor a web service, mail service, disk space on 2 disks, memory and CPU usage on each of 80 systems). You should buy the license for a minimum: 6x80=480 test items. In this case Professional package is good enough. This license allows you to install future versions of the HostMonitor, MIB Browser, Process Meter, WMI Explorer and Log Analyzer released within next 6 months.

How many licenses do you need?

The single license allows you to install HostMonitor on ONE system. However using just one instance of HostMonitor you may monitor many remote systems. If you want to run (install) HostMonitor on a number of systems then you have to buy the same number of licenses. The same rule is applicable to any of the auxiliary tools of Advanced Host Monitor package. Example: if you want to install HostMonitor on 1 system and start Remote Monitoring Agent on 5 different systems, you need 1 license for HostMonitor and 5 RMA licenses (usually single RMA can monitor entire LAN).