GLPI is fully open source; however, to take advantage of everything GLPI has to offer, you can join the GLPI Network. The GLPI Network provides three main benefits:
You can read more about the GLPI Network from Teclib' (developers of GLPI) here.
If you would like a hosted/SaaS version of GLPI, you can join the GLPI Network Cloud. You get all the benefits of GLPI Network, with the peace of mind of a fully managed infrastructure.
For self-hosted (e.g., on-premise) GLPI installations, you can join with a subscription sized according to the number of IT agents and assets in your system. This includes all GLPI Network benefits without having to give up any control over your infrastructure.